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From l..@apache.org
Subject svn commit: r1311904 [1/2] - in /commons/proper/collections/trunk: ./ src/main/java/org/apache/commons/collections/ src/main/java/org/apache/commons/collections/functors/ src/main/java/org/apache/commons/collections/list/difference/ src/test/java/org/a...
Date Tue, 10 Apr 2012 18:22:30 GMT
Author: luc
Date: Tue Apr 10 18:22:29 2012
New Revision: 1311904

URL: http://svn.apache.org/viewvc?rev=1311904&view=rev
Log:
Added an implementation of Eugene Myers difference algorithm.

JIRA: COLLECTIONS-404

Added:
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/CommandVisitor.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/DeleteCommand.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditCommand.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditScript.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/InsertCommand.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/KeepCommand.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsFinder.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsHandler.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/SequencesComparator.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/Snake.java   (with props)
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/package.html   (with props)
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/list/difference/
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/list/difference/SequencesComparatorTest.java   (with props)
Modified:
    commons/proper/collections/trunk/pom.xml
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/IndexedCollection.java
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/CatchAndRethrowClosure.java
    commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/ComparatorPredicate.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/AbstractDecoratedCollectionTest.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/MockTestCase.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestIndexedCollection.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/functors/BasicClosureTestBase.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/functors/TestCatchAndRethrowClosure.java
    commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/functors/TestComparatorPredicate.java

Modified: commons/proper/collections/trunk/pom.xml
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/pom.xml?rev=1311904&r1=1311903&r2=1311904&view=diff
==============================================================================
--- commons/proper/collections/trunk/pom.xml (original)
+++ commons/proper/collections/trunk/pom.xml Tue Apr 10 18:22:29 2012
@@ -227,6 +227,9 @@
       <name>Berin Loritsch</name>
     </contributor>
     <contributor>
+      <name>Luc Maisonobe</name>
+    </contributor>
+    <contributor>
       <name>Hendrik Maryns</name>
     </contributor>
     <contributor>

Modified: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/IndexedCollection.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/IndexedCollection.java?rev=1311904&r1=1311903&r2=1311904&view=diff
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/IndexedCollection.java (original)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/IndexedCollection.java Tue Apr 10 18:22:29 2012
@@ -1,136 +1,136 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.commons.collections;
-
-import java.util.Collection;
-import java.util.HashMap;
-
-import org.apache.commons.collections.collection.AbstractCollectionDecorator;
-
-/**
- * An IndexedCollection is a Map-like view onto a Collection. It accepts a
- * keyTransformer to define how the keys are converted from the values.
- * <p>
- * Modifications made to this decorator modify the index as well as the
- * decorated {@link Collection}. However, modifications to the underlying
- * {@link Collection} will not updated the index and it will get out of sync.
- * <p>
- * If modification to the decorated {@link Collection} is unavoidable, then a
- * call to {@link #reindex()} will update the index to the current contents of
- * the {@link Collection}.
- *
- * @param <K> the type of object in the index.
- * @param <C> the type of object in the collection.
- * @author Stephen Kestle
- */
-// TODO support MultiMap/non-unique index behavior
-// TODO add support for remove and clear
-public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
-    /**
-     * .
-     */
-    private static final long serialVersionUID = -5512610452568370038L;
-
-    /**
-     * Create an {@link IndexedCollection} for a unique index.
-     *
-     * @param <K> the index object type.
-     * @param <C> the collection type.
-     * @param coll the decorated {@link Collection}.
-     * @param keyTransformer the {@link Transformer} for generating index keys.
-     * @return the created {@link IndexedCollection}.
-     */
-    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
-        return new IndexedCollection<K, C>(coll, keyTransformer, new HashMap<K, C>());
-    }
-
-    /**
-     * The {@link Transformer} for generating index keys.
-     */
-    private final Transformer<C, K> keyTransformer;
-
-    /**
-     * The map of indexes to collected objects.
-     */
-    private final HashMap<K, C> index;
-
-    /**
-     * Create a {@link IndexedCollection} for a unique index.
-     *
-     * @param coll the decorated {@link Collection}.
-     * @param keyTransformer the {@link Transformer} for generating index keys.
-     */
-    public IndexedCollection(Collection<C> coll, Transformer<C, K> keyTransformer, HashMap<K, C> map) {
-        super(coll);
-        this.keyTransformer = keyTransformer;
-        this.index = map;
-        reindex();
-    }
-
-    /**
-     * Clears the index and re-indexes the entire decorated {@link Collection}.
-     */
-    public void reindex() {
-        index.clear();
-        for (C c : decorated()) {
-            addIndex(c);
-        }
-    }
-
-    /**
-     * Adds an object to the collection and index.
-     */
-    @Override
-    // TODO: Add error handling for when super.add() fails
-    public boolean add(C object) {
-        addIndex(object);
-        return super.add(object);
-    }
-
-    /**
-     * Adds an entire collection to the collection and index.
-     */
-    @Override
-    // TODO: Add error handling for when super.addAll() fails
-    public boolean addAll(Collection<? extends C> coll) {
-        for (C c : coll) {
-            addIndex(c);
-        }
-        return super.addAll(coll);
-    }
-
-    /**
-     * Provides checking for adding the index.
-     *
-     * @param object the object to index.
-     */
-    private void addIndex(C object) {
-        final C existingObject = index.put(keyTransformer.transform(object), object);
-        if (existingObject != null) {
-            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
-        }
-    }
-
-    /**
-     * Get the element associated with the given key.
-     * @param key to look up
-     * @return element found
-     */
-    public C get(K key) {
-        return index.get(key);
-    }
-}
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections;
+
+import java.util.Collection;
+import java.util.HashMap;
+
+import org.apache.commons.collections.collection.AbstractCollectionDecorator;
+
+/**
+ * An IndexedCollection is a Map-like view onto a Collection. It accepts a
+ * keyTransformer to define how the keys are converted from the values.
+ * <p>
+ * Modifications made to this decorator modify the index as well as the
+ * decorated {@link Collection}. However, modifications to the underlying
+ * {@link Collection} will not updated the index and it will get out of sync.
+ * <p>
+ * If modification to the decorated {@link Collection} is unavoidable, then a
+ * call to {@link #reindex()} will update the index to the current contents of
+ * the {@link Collection}.
+ *
+ * @param <K> the type of object in the index.
+ * @param <C> the type of object in the collection.
+ * @author Stephen Kestle
+ */
+// TODO support MultiMap/non-unique index behavior
+// TODO add support for remove and clear
+public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
+    /**
+     * .
+     */
+    private static final long serialVersionUID = -5512610452568370038L;
+
+    /**
+     * Create an {@link IndexedCollection} for a unique index.
+     *
+     * @param <K> the index object type.
+     * @param <C> the collection type.
+     * @param coll the decorated {@link Collection}.
+     * @param keyTransformer the {@link Transformer} for generating index keys.
+     * @return the created {@link IndexedCollection}.
+     */
+    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
+        return new IndexedCollection<K, C>(coll, keyTransformer, new HashMap<K, C>());
+    }
+
+    /**
+     * The {@link Transformer} for generating index keys.
+     */
+    private final Transformer<C, K> keyTransformer;
+
+    /**
+     * The map of indexes to collected objects.
+     */
+    private final HashMap<K, C> index;
+
+    /**
+     * Create a {@link IndexedCollection} for a unique index.
+     *
+     * @param coll the decorated {@link Collection}.
+     * @param keyTransformer the {@link Transformer} for generating index keys.
+     */
+    public IndexedCollection(Collection<C> coll, Transformer<C, K> keyTransformer, HashMap<K, C> map) {
+        super(coll);
+        this.keyTransformer = keyTransformer;
+        this.index = map;
+        reindex();
+    }
+
+    /**
+     * Clears the index and re-indexes the entire decorated {@link Collection}.
+     */
+    public void reindex() {
+        index.clear();
+        for (C c : decorated()) {
+            addIndex(c);
+        }
+    }
+
+    /**
+     * Adds an object to the collection and index.
+     */
+    @Override
+    // TODO: Add error handling for when super.add() fails
+    public boolean add(C object) {
+        addIndex(object);
+        return super.add(object);
+    }
+
+    /**
+     * Adds an entire collection to the collection and index.
+     */
+    @Override
+    // TODO: Add error handling for when super.addAll() fails
+    public boolean addAll(Collection<? extends C> coll) {
+        for (C c : coll) {
+            addIndex(c);
+        }
+        return super.addAll(coll);
+    }
+
+    /**
+     * Provides checking for adding the index.
+     *
+     * @param object the object to index.
+     */
+    private void addIndex(C object) {
+        final C existingObject = index.put(keyTransformer.transform(object), object);
+        if (existingObject != null) {
+            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
+        }
+    }
+
+    /**
+     * Get the element associated with the given key.
+     * @param key to look up
+     * @return element found
+     */
+    public C get(K key) {
+        return index.get(key);
+    }
+}

Modified: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/CatchAndRethrowClosure.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/CatchAndRethrowClosure.java?rev=1311904&r1=1311903&r2=1311904&view=diff
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/CatchAndRethrowClosure.java (original)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/CatchAndRethrowClosure.java Tue Apr 10 18:22:29 2012
@@ -1,76 +1,76 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.commons.collections.functors;
-
-import org.apache.commons.collections.Closure;
-import org.apache.commons.collections.FunctorException;
-
-/**
- * {@link Closure} that catches any checked exception and re-throws it as a
- * {@link FunctorException} runtime exception. Example usage:
- * 
- * <pre>
- * // Create a catch and re-throw closure via anonymous subclass
- * CatchAndRethrowClosure&lt;String&gt; writer = new ThrowingClosure() {
- *     private java.io.Writer out = // some writer
- *     
- *     protected void executeAndThrow(String input) throws IOException {
- *         out.write(input); // throwing of IOException allowed
- *     }
- * };
- * 
- * // use catch and re-throw closure
- * java.util.List<String> strList = // some list
- * try {
- *     CollctionUtils.forAllDo(strList, writer);
- * } catch (FunctorException ex) {
- *     Throwable originalError = ex.getCause();
- *     // handle error
- * }
- * </pre>
- * 
- * @since Commons Collections 4.0
- * @version $Revision$
- */
-public abstract class CatchAndRethrowClosure<E> implements Closure<E> {
-
-    /**
-     * Execute this closure on the specified input object.
-     * 
-     * @param input the input to execute on
-     * @throws FunctorException (runtime) if the closure execution resulted in a
-     *             checked exception.
-     */
-    public void execute(E input) {
-        try {
-            executeAndThrow(input);
-        } catch (RuntimeException ex) {
-            throw ex;
-        } catch (Throwable t) {
-            throw new FunctorException(t);
-        }
-    }
-
-    /**
-     * Execute this closure on the specified input object.
-     * 
-     * @param input the input to execute on
-     * @throws Throwable if the closure execution resulted in a checked
-     *             exception.
-     */
-    protected abstract void executeAndThrow(E input) throws Throwable;
-}
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.functors;
+
+import org.apache.commons.collections.Closure;
+import org.apache.commons.collections.FunctorException;
+
+/**
+ * {@link Closure} that catches any checked exception and re-throws it as a
+ * {@link FunctorException} runtime exception. Example usage:
+ * 
+ * <pre>
+ * // Create a catch and re-throw closure via anonymous subclass
+ * CatchAndRethrowClosure&lt;String&gt; writer = new ThrowingClosure() {
+ *     private java.io.Writer out = // some writer
+ *     
+ *     protected void executeAndThrow(String input) throws IOException {
+ *         out.write(input); // throwing of IOException allowed
+ *     }
+ * };
+ * 
+ * // use catch and re-throw closure
+ * java.util.List<String> strList = // some list
+ * try {
+ *     CollctionUtils.forAllDo(strList, writer);
+ * } catch (FunctorException ex) {
+ *     Throwable originalError = ex.getCause();
+ *     // handle error
+ * }
+ * </pre>
+ * 
+ * @since Commons Collections 4.0
+ * @version $Revision$
+ */
+public abstract class CatchAndRethrowClosure<E> implements Closure<E> {
+
+    /**
+     * Execute this closure on the specified input object.
+     * 
+     * @param input the input to execute on
+     * @throws FunctorException (runtime) if the closure execution resulted in a
+     *             checked exception.
+     */
+    public void execute(E input) {
+        try {
+            executeAndThrow(input);
+        } catch (RuntimeException ex) {
+            throw ex;
+        } catch (Throwable t) {
+            throw new FunctorException(t);
+        }
+    }
+
+    /**
+     * Execute this closure on the specified input object.
+     * 
+     * @param input the input to execute on
+     * @throws Throwable if the closure execution resulted in a checked
+     *             exception.
+     */
+    protected abstract void executeAndThrow(E input) throws Throwable;
+}

Modified: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/ComparatorPredicate.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/ComparatorPredicate.java?rev=1311904&r1=1311903&r2=1311904&view=diff
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/ComparatorPredicate.java (original)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/functors/ComparatorPredicate.java Tue Apr 10 18:22:29 2012
@@ -1,188 +1,188 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.commons.collections.functors;
-
-import java.io.Serializable;
-import java.util.Comparator;
-
-import org.apache.commons.collections.Predicate;
-
-/**
- * Predicate that compares the input object with the one stored in the predicate using a comparator.
- * In addition, the comparator result can be evaluated in accordance to a supplied criterion value.
- *
- * In order to demonstrate the use of the predicate, the following variables are declared:
- *
- * <pre>
- * Integer ONE = new Integer(1);
- * Integer TWO = new Integer(2);
- *
- * Comparator comparator = new Comparator() {
- *
- *     public int compare(Object first, Object second) {
- *         return ((Integer) second) - ((Integer) first);
- *     }
- *
- * };
- * </pre>
- *
- * Using the declared variables, the <code>ComparatorPredicate</code> can be used used in the
- * following way:
- *
- * <pre>
- * ComparatorPredicate.getInstance(ONE, comparator).evaluate(TWO);
- * </pre>
- *
- * The input variable <code>TWO</code> in compared to the stored variable <code>ONE</code> using
- * the supplied <code>comparator</code>. This is the default usage of the predicate and will return
- * <code>true</code> if the underlying comparator returns <code>0</code>. In addition to the default
- * usage of the predicate, it is possible to evaluate the comparator's result in several ways. The
- * following {@link Criterion} enumeration values are provided by the predicate:
- * </p>
- *
- * <ul>
- *     <li>EQUAL</li>
- *     <li>GREATER</li>
- *     <li>GREATER_OR_EQUAL</li>
- *     <li>LESS</li>
- *     <li>LESS_OR_EQUAL</li>
- * </ul>
- *
- * The following examples demonstrates how these constants can be used in order to manipulate the
- * evaluation of a comparator result.
- *
- * <pre>
- * ComparatorPredicate.getInstance(ONE, comparator, <b>ComparatorPredicate.Criterion.GREATER</b>).evaluate(TWO);
- * </pre>
- *
- * The input variable TWO is compared to the stored variable ONE using the supplied <code>comparator</code>
- * using the <code>GREATER</code> evaluation criterion constant. This instructs the predicate to
- * return <code>true</code> if the comparator returns a value greater than <code>0</code>.
- *
- * @since Commons Collections 4.0
- * @version $Revision$
- *
- * @author Rune Peter Bjørnstad.
- */
-public class ComparatorPredicate<T> implements Predicate<T>, Serializable {
-
-    private static final long serialVersionUID = -1863209236504077399L;
-
-    public enum Criterion {
-        EQUAL, GREATER, LESS, GREATER_OR_EQUAL, LESS_OR_EQUAL,
-    }
-
-    // Instance variables:
-
-    /** The internal object to compare with */
-    private final T object;
-
-    /** The comparator to use for comparison */
-    private final Comparator<T> comparator;
-
-    /** The comparison evaluation criterion to use */
-    private final Criterion criterion;
-
-    /**
-     * Factory to create the comparator predicate
-     *
-     * @param object  the object to compare to
-     * @param comparator  the comparator to use for comparison
-     * @return the predicate
-     * @throws IllegalArgumentException if comparator is null
-     */
-    public static <T> Predicate<T> comparatorPredicate(T object, Comparator<T> comparator) {
-        return comparatorPredicate(object, comparator, Criterion.EQUAL);
-    }
-
-    /**
-     * Factory to create the comparator predicate
-     *
-     * @param object  the object to compare to
-     * @param comparator  the comparator to use for comparison
-     * @param criterion  the criterion to use to evaluate comparison
-     * @return the predicate
-     * @throws IllegalArgumentException if comparator is null of criterion is invalid
-     */
-    public static <T> Predicate<T> comparatorPredicate(T object, Comparator<T> comparator, Criterion criterion) {
-        if (comparator == null) {
-            throw new IllegalArgumentException("Comparator must not be null.");
-        }
-        if (criterion == null) {
-            throw new IllegalArgumentException("Criterion must not be null.");
-        }
-        return new ComparatorPredicate<T>(object, comparator, criterion);
-    }
-
-    /**
-     * Constructor that performs no validation.
-     * Use <code>getInstance</code> if you want.
-     *
-     * @param object  the object to compare to
-     * @param comparator  the comparator to use for comparison
-     * @param criterion  the criterion to use to evaluate comparison
-     */
-    public ComparatorPredicate(T object, Comparator<T> comparator, Criterion criterion) {
-        super();
-        this.object = object;
-        this.comparator = comparator;
-        this.criterion = criterion;
-    }
-
-    /**
-     * Evaluates the predicate. The predicate evaluates to <code>true</code> in the following cases:
-     *
-     * <ul>
-     *     <li><code>comparator.compare(object, input) == 0 && criterion == EQUAL</code></li>
-     *     <li><code>comparator.compare(object, input) < 0 && criterion == LESS</code></li>
-     *     <li><code>comparator.compare(object, input) > 0 && criterion == GREATER</code></li>
-     *     <li><code>comparator.compare(object, input) >= 0 && criterion == GREATER_OR_EQUAL</code></li>
-     *     <li><code>comparator.compare(object, input) <= 0 && criterion == LESS_OR_EQUAL</code></li>
-     * </ul>
-     *
-     * @see org.apache.commons.collections.Predicate#evaluate(java.lang.Object)
-     * @see java.util.Comparator#compare(java.lang.Object first, java.lang.Object second)
-     *
-     * @throws IllegalStateException if the criterion is invalid (really not possible)
-     */
-    public boolean evaluate(T target) {
-
-        boolean result = false;
-        int comparison = comparator.compare(object, target);
-        switch (criterion) {
-        case EQUAL:
-            result = (comparison == 0);
-            break;
-        case GREATER:
-            result = (comparison > 0);
-            break;
-        case LESS:
-            result = (comparison < 0);
-            break;
-        case GREATER_OR_EQUAL:
-            result = (comparison >= 0);
-            break;
-        case LESS_OR_EQUAL:
-            result = (comparison <= 0);
-            break;
-        default:
-            throw new IllegalStateException("The current criterion '" + criterion + "' is invalid.");
-        }
-
-        return result;
-    }
-}
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.functors;
+
+import java.io.Serializable;
+import java.util.Comparator;
+
+import org.apache.commons.collections.Predicate;
+
+/**
+ * Predicate that compares the input object with the one stored in the predicate using a comparator.
+ * In addition, the comparator result can be evaluated in accordance to a supplied criterion value.
+ *
+ * In order to demonstrate the use of the predicate, the following variables are declared:
+ *
+ * <pre>
+ * Integer ONE = new Integer(1);
+ * Integer TWO = new Integer(2);
+ *
+ * Comparator comparator = new Comparator() {
+ *
+ *     public int compare(Object first, Object second) {
+ *         return ((Integer) second) - ((Integer) first);
+ *     }
+ *
+ * };
+ * </pre>
+ *
+ * Using the declared variables, the <code>ComparatorPredicate</code> can be used used in the
+ * following way:
+ *
+ * <pre>
+ * ComparatorPredicate.getInstance(ONE, comparator).evaluate(TWO);
+ * </pre>
+ *
+ * The input variable <code>TWO</code> in compared to the stored variable <code>ONE</code> using
+ * the supplied <code>comparator</code>. This is the default usage of the predicate and will return
+ * <code>true</code> if the underlying comparator returns <code>0</code>. In addition to the default
+ * usage of the predicate, it is possible to evaluate the comparator's result in several ways. The
+ * following {@link Criterion} enumeration values are provided by the predicate:
+ * </p>
+ *
+ * <ul>
+ *     <li>EQUAL</li>
+ *     <li>GREATER</li>
+ *     <li>GREATER_OR_EQUAL</li>
+ *     <li>LESS</li>
+ *     <li>LESS_OR_EQUAL</li>
+ * </ul>
+ *
+ * The following examples demonstrates how these constants can be used in order to manipulate the
+ * evaluation of a comparator result.
+ *
+ * <pre>
+ * ComparatorPredicate.getInstance(ONE, comparator, <b>ComparatorPredicate.Criterion.GREATER</b>).evaluate(TWO);
+ * </pre>
+ *
+ * The input variable TWO is compared to the stored variable ONE using the supplied <code>comparator</code>
+ * using the <code>GREATER</code> evaluation criterion constant. This instructs the predicate to
+ * return <code>true</code> if the comparator returns a value greater than <code>0</code>.
+ *
+ * @since Commons Collections 4.0
+ * @version $Revision$
+ *
+ * @author Rune Peter Bjørnstad.
+ */
+public class ComparatorPredicate<T> implements Predicate<T>, Serializable {
+
+    private static final long serialVersionUID = -1863209236504077399L;
+
+    public enum Criterion {
+        EQUAL, GREATER, LESS, GREATER_OR_EQUAL, LESS_OR_EQUAL,
+    }
+
+    // Instance variables:
+
+    /** The internal object to compare with */
+    private final T object;
+
+    /** The comparator to use for comparison */
+    private final Comparator<T> comparator;
+
+    /** The comparison evaluation criterion to use */
+    private final Criterion criterion;
+
+    /**
+     * Factory to create the comparator predicate
+     *
+     * @param object  the object to compare to
+     * @param comparator  the comparator to use for comparison
+     * @return the predicate
+     * @throws IllegalArgumentException if comparator is null
+     */
+    public static <T> Predicate<T> comparatorPredicate(T object, Comparator<T> comparator) {
+        return comparatorPredicate(object, comparator, Criterion.EQUAL);
+    }
+
+    /**
+     * Factory to create the comparator predicate
+     *
+     * @param object  the object to compare to
+     * @param comparator  the comparator to use for comparison
+     * @param criterion  the criterion to use to evaluate comparison
+     * @return the predicate
+     * @throws IllegalArgumentException if comparator is null of criterion is invalid
+     */
+    public static <T> Predicate<T> comparatorPredicate(T object, Comparator<T> comparator, Criterion criterion) {
+        if (comparator == null) {
+            throw new IllegalArgumentException("Comparator must not be null.");
+        }
+        if (criterion == null) {
+            throw new IllegalArgumentException("Criterion must not be null.");
+        }
+        return new ComparatorPredicate<T>(object, comparator, criterion);
+    }
+
+    /**
+     * Constructor that performs no validation.
+     * Use <code>getInstance</code> if you want.
+     *
+     * @param object  the object to compare to
+     * @param comparator  the comparator to use for comparison
+     * @param criterion  the criterion to use to evaluate comparison
+     */
+    public ComparatorPredicate(T object, Comparator<T> comparator, Criterion criterion) {
+        super();
+        this.object = object;
+        this.comparator = comparator;
+        this.criterion = criterion;
+    }
+
+    /**
+     * Evaluates the predicate. The predicate evaluates to <code>true</code> in the following cases:
+     *
+     * <ul>
+     *     <li><code>comparator.compare(object, input) == 0 && criterion == EQUAL</code></li>
+     *     <li><code>comparator.compare(object, input) < 0 && criterion == LESS</code></li>
+     *     <li><code>comparator.compare(object, input) > 0 && criterion == GREATER</code></li>
+     *     <li><code>comparator.compare(object, input) >= 0 && criterion == GREATER_OR_EQUAL</code></li>
+     *     <li><code>comparator.compare(object, input) <= 0 && criterion == LESS_OR_EQUAL</code></li>
+     * </ul>
+     *
+     * @see org.apache.commons.collections.Predicate#evaluate(java.lang.Object)
+     * @see java.util.Comparator#compare(java.lang.Object first, java.lang.Object second)
+     *
+     * @throws IllegalStateException if the criterion is invalid (really not possible)
+     */
+    public boolean evaluate(T target) {
+
+        boolean result = false;
+        int comparison = comparator.compare(object, target);
+        switch (criterion) {
+        case EQUAL:
+            result = (comparison == 0);
+            break;
+        case GREATER:
+            result = (comparison > 0);
+            break;
+        case LESS:
+            result = (comparison < 0);
+            break;
+        case GREATER_OR_EQUAL:
+            result = (comparison >= 0);
+            break;
+        case LESS_OR_EQUAL:
+            result = (comparison <= 0);
+            break;
+        default:
+            throw new IllegalStateException("The current criterion '" + criterion + "' is invalid.");
+        }
+
+        return result;
+    }
+}

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+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/CommandVisitor.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,148 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+
+/** This interface should be implemented by user object to walk
+ * through {@link EditScript EditScript} objects.
+
+ * <p>Users should implement this interface in order to walk through
+ * the {@link EditScript EditScript} object created by the comparison
+ * of two sequences. This is a direct application of the visitor
+ * design pattern. The {@link EditScript#visit EditScript.visit}
+ * method takes an object implementing this interface as an argument,
+ * it will perform the loop over all commands in the script and the
+ * proper methods of the user class will be called as the commands are
+ * encountered.</p>
+
+ * <p>The implementation of the user visitor class will depend on the
+ * need. Here are two examples.
+ * </p>
+ * 
+ * <p>
+ * The first example is a visitor that build the longest common
+ * subsequence:
+ * <pre>
+ * import org.apache.commons.collections.list.difference.CommandVisitor;
+ * 
+ * import java.util.ArrayList;
+ *
+ * public class LongestCommonSubSequence implements CommandVisitor {
+ * 
+ *   public LongestCommonSubSequence() {
+ *     a = new ArrayList();
+ *   }
+ * 
+ *   public void visitInsertCommand(Object object) {
+ *   }
+ * 
+ *   public void visitKeepCommand(Object object) {
+ *     a.add(object);
+ *   }
+ * 
+ *   public void visitDeleteCommand(Object object) {
+ *   }
+ * 
+ *   public Object[] getSubSequence() {
+ *     return a.toArray();
+ *   }
+ * 
+ *   private arrayList a;
+ * 
+ * }
+ * </pre>
+ * </p>
+ * 
+ * <p>
+ * The second example is a visitor that shows the commands and the way
+ * they transform the first sequence into the second one:
+ * <pre>
+ * import org.apache.commons.collections.list.difference.CommandVisitor;
+ * 
+ * import java.util.Arrays;
+ * import java.util.ArrayList;
+ * import java.util.Iterator;
+ *
+ * public class ShowVisitor implements CommandVisitor {
+ * 
+ *   public ShowVisitor(Object[] sequence1) {
+ *     v = new ArrayList();
+ *     v.addAll(Arrays.asList(sequence1));
+ *     index = 0;
+ *   }
+ * 
+ *   public void visitInsertCommand(Object object) {
+ *     v.insertElementAt(object, index++);
+ *     display("insert", object);
+ *   }
+ * 
+ *   public void visitKeepCommand(Object object) {
+ *     ++index;
+ *     display("keep  ", object);
+ *   }
+ * 
+ *   public void visitDeleteCommand(Object object) {
+ *     v.remove(index);
+ *     display("delete", object);
+ *   }
+ * 
+ *   private void display(String commandName, Object object) {
+ *     System.out.println(commandName + " " + object + " ->" + this);
+ *   }
+ * 
+ *   public String toString() {
+ *     StringBuffer buffer = new StringBuffer();
+ *     for (Iterator iter = v.iterator(); iter.hasNext();) {
+ *       buffer.append(' ').append(iter.next());
+ *     }
+ *     return buffer.toString();
+ *   }
+ * 
+ *   private ArrayList v;
+ *   private int index;
+ * 
+ * }
+ * </pre>
+ * </p>
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+
+ */
+public interface CommandVisitor<T> {
+
+    /** Method called when an insert command is encountered.
+     * @param object object to insert (this object comes from the
+     * second sequence)
+     */
+    void visitInsertCommand(T object);
+
+    /** Method called when a keep command is encountered.
+     * @param object object to keep (this object comes from the
+     * first sequence)
+     */
+    void visitKeepCommand(T object);
+
+    /** Method called when a delete command is encountered.
+     * @param object object to delete (this object comes from the
+     * first sequence)
+     */
+    void visitDeleteCommand(T object);
+
+}

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--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/DeleteCommand.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/DeleteCommand.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,56 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+
+/** Command representing the deletion of one object of the first sequence.
+
+ * When one object of the first sequence has no corresponding object
+ * in the second sequence at the right place, the {@link EditScript
+ * edit script} transforming the first sequence into the second
+ * sequence uses an instance of this class to represent the deletion
+ * of this object. The objects embedded in these type of commands
+ * always come from the first sequence.
+
+ * @see SequencesComparator
+ * @see EditScript
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public class DeleteCommand<T> extends EditCommand<T> {
+    
+    /** Simple constructor.
+     * Creates a new instance of DeleteCommand
+     * @param object the object of the first sequence that should be deleted
+     */
+    public DeleteCommand(T object) {
+      super(object);
+    }
+    
+    /** Accept a visitor.
+     * When a <code>DeleteCommand</code> accepts a visitor, it calls
+     * its {@link CommandVisitor#visitDeleteCommand
+     * visitDeleteCommand} method.
+     * @param visitor the visitor to be accepted
+     */    
+    public void accept(CommandVisitor<T> visitor) {
+      visitor.visitDeleteCommand(object);
+    }    
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditCommand.java
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--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditCommand.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditCommand.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,76 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+
+/** Abstract base class for all commands used to transform an objects
+ *  sequence into another one.
+
+ * <p>When two objects sequences are compared through the {@link
+ * SequencesComparator#getScript SequencesComparator.getScript}
+ * method, the result is provided has a {@link EditScript script}
+ * containing the commands that progressively transform the first
+ * sequence into the second one.</p>
+
+ * <p>There are only three types of commands, all of which are
+ * subclasses of this abstract class. Each command is associated with
+ * one object belonging to at least one of the sequences. These
+ * commands are {@link InsertCommand InsertCommand} which correspond
+ * to an object of the second sequence beeing inserted into the first
+ * sequence, {@link DeleteCommand DeleteCommand} which correspond to
+ * an object of the first sequence beeing removed and {@link
+ * KeepCommand KeepCommand} which correspond to an object of the first
+ * sequence which <code>equals</code> an object in the second
+ * sequence. It is guaranteed that comparison is always performed this
+ * way (i.e. the <code>equals</code> method of the object from the
+ * first sequence is used and the object passed as an argument comes
+ * from the second sequence) ; this can be important if subclassing is
+ * used for some elements in the first sequence and the
+ * <code>equals</code> method is specialized.</p>
+
+ * @see SequencesComparator
+ * @see EditScript
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public abstract class EditCommand<T> {
+
+  /** Simple constructor.
+   * Creates a new instance of EditCommand
+   * @param object reference to the object associated with this
+   * command, this refers to an element of one of the sequences
+   * beeing compared
+   */
+  protected EditCommand(T object) {
+    this.object = object;
+  }
+    
+  /** Accept a visitor.
+   * This method is invoked for each commands belonging to an {@link
+   * EditScript EditScript}, in order to implement the visitor
+   * design pattern
+   * @param visitor the visitor to be accepted
+   */    
+  public abstract void accept(CommandVisitor<T> visitor);
+    
+  /** Object on which the command should be applied. */
+  protected T object;
+    
+}

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--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditScript.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/EditScript.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,126 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ *  This class gathers all the {@link EditCommand commands} needed to
+ *  transform one objects sequence into another objects sequence.
+
+ * <p>An edit script is the most general view of the differences
+ * between two sequences. It is built as the result of the comparison
+ * between two sequences by the {@link SequencesComparator
+ * SequencesComparator} class. The user can walk through it using
+ * the <em>visitor</em> design pattern.</p>
+
+ * <p>It is guaranteed that the objects embedded in the {@link
+ * InsertCommand insert commands} come from the second sequence and
+ * that the objects embedded in either the {@link DeleteCommand delete
+ * commands} or {@link KeepCommand keep commands} come from the first
+ * sequence. This can be important if subclassing is used for some
+ * elements in the first sequence and the <code>equals</code> method
+ * is specialized.</p>
+
+ * @see SequencesComparator
+ * @see EditCommand
+ * @see CommandVisitor
+ * @see ReplacementsHandler
+ *
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public class EditScript<T> {
+
+  /** Container for the commands. */
+  private List<EditCommand<T>> commands;
+
+  /** Length of the longest common subsequence. */
+  private int lcsLength;
+
+  /** Number of modifications. */
+  private int modifications;
+
+  /** Simple constructor.
+   * Creates a new empty script.
+   */
+  public EditScript() {
+    commands      = new ArrayList<EditCommand<T>>();
+    lcsLength     = 0;
+    modifications = 0;
+  }
+
+  /** Add a keep command to the script.
+   * @param command command to add
+   */
+  public void append(KeepCommand<T> command) {
+    commands.add(command);
+    ++lcsLength;
+  }
+
+  /** Add an insert command to the script.
+   * @param command command to add
+   */
+  public void append(InsertCommand<T> command) {
+    commands.add(command);
+    ++modifications;
+  }
+
+  /** Add a delete command to the script.
+   * @param command command to add
+   */
+  public void append(DeleteCommand<T> command) {
+    commands.add(command);
+    ++modifications;
+  }
+
+  /** Visit the script.
+   * The script implements the <em>visitor</em> design pattern, this
+   * method is the entry point to which the user supplies its own
+   * visitor, the script will be responsible to drive it through the
+   * commands in order and call the appropriate method as each
+   * command is encountered.
+   * @param visitor the visitor that will visit all commands in turn
+   */
+  public void visit(CommandVisitor<T> visitor) {
+    for (EditCommand<T> command : commands) {
+      command.accept(visitor);
+    }
+  }
+
+  /** Get the length of the Longest Common Subsequence (LCS).
+   * The length of the longest common subsequence is the number of
+   * {@link KeepCommand keep commands} in the script.
+   * @return length of the Longest Common Subsequence
+   */
+  public int getLCSLength() {
+    return lcsLength;
+  }
+
+  /** Get the number of effective modifications.
+   * The number of effective modification is the number of {@link
+   * DeleteCommand delete} and {@link InsertCommand insert} commands
+   * in the script.
+   * @return number of effective modifications
+   */
+  public int getModifications() {
+    return modifications;
+  }
+
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/InsertCommand.java
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==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/InsertCommand.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/InsertCommand.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+
+/** Command representing the insertion of one object of the second sequence.
+
+ * When one object of the second sequence has no corresponding object
+ * in the first sequence at the right place, the {@link EditScript
+ * edit script} transforming the first sequence into the second
+ * sequence uses an instance of this class to represent the insertion
+ * of this object. The objects embedded in these type of commands
+ * always come from the second sequence.
+
+ * @see SequencesComparator
+ * @see EditScript
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public class InsertCommand<T> extends EditCommand<T> {
+    
+    /** Simple constructor.
+     * Creates a new instance of InsertCommand
+     * @param object the object of the second sequence that should be inserted
+     */
+    public InsertCommand(T object) {
+      super(object);
+    }
+    
+    /** Accept a visitor.
+     * When an <code>InsertCommand</code> accepts a visitor, it calls
+     * its {@link CommandVisitor#visitInsertCommand
+     * visitInsertCommand} method.
+     * @param visitor the visitor to be accepted
+     */    
+    public void accept(CommandVisitor<T> visitor) {
+      visitor.visitInsertCommand(object);
+    }
+    
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/KeepCommand.java
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==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/KeepCommand.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/KeepCommand.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+
+/** Command representing the keeping of one object present in both sequences.
+
+ * When one object of the first sequence <code>equals</code> another
+ * objects in the second sequence at the right place, the {@link
+ * EditScript edit script} transforming the first sequence into the
+ * second sequence uses an instance of this class to represent the
+ * keeping of this object. The objects embedded in these type of
+ * commands always come from the first sequence.
+
+ * @see SequencesComparator
+ * @see EditScript
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public class KeepCommand<T> extends EditCommand<T> {
+    
+    /** Simple constructor.
+     * Creates a new instance of KeepCommand
+     * @param object the object belonging to both sequences (the
+     * object is a reference to the instance in the first sequence
+     * which is known to be equal to an instance in the second
+     * sequence)
+     */
+    public KeepCommand(T object) {
+      super(object);
+    }
+
+    /** Accept a visitor.
+     * When a <code>KeepCommand</code> accepts a visitor, it calls
+     * its {@link CommandVisitor#visitKeepCommand visitKeepCommand} method.
+     * @param visitor the visitor to be accepted
+     */    
+    public void accept(CommandVisitor<T> visitor) {
+      visitor.visitKeepCommand(object);
+    }
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsFinder.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsFinder.java?rev=1311904&view=auto
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsFinder.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsFinder.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,107 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class handles sequences of replacements resulting from a
+ * comparison.
+
+ * <p>The comparison of two objects sequences leads to the
+ * identification of common parts and parts which only belong to the
+ * first or to the second sequence. The common parts appear in the
+ * edit script in the form of <em>keep</em> commands, they can be considered
+ * as synchronization objects between the two sequences. These
+ * synchronization objects split the two sequences in synchronized
+ * sub-sequences. The first sequence can be transformed into the second
+ * one by replacing each synchronized sub-sequence of the first
+ * sequence by the corresponding sub-sequence of the second
+ * sequence. This is a synthetic way to see an {@link EditScript edit
+ * script}, replacing individual {@link DeleteCommand delete}, {@link
+ * KeepCommand keep} and {@link InsertCommand insert} commands by
+ * fewer replacements acting on complete sub-sequences.</p>
+
+ * <p>This class is devoted to perform this interpretation. It visits
+ * an {@link EditScript edit script} (because it implements the {@link
+ * CommandVisitor CommandVisitor} interface) and calls a user-supplied
+ * handler implementing the {@link ReplacementsHandler
+ * ReplacementsHandler} interface to process the sub-sequences.</p>
+
+ * @see ReplacementsHandler
+ * @see EditScript
+ * @see SequencesComparator
+ 
+ * @since 4.0
+ * @author Luc Maisonobe
+ * @author Jordane Sarda
+ * @version $Id$
+ */
+public class ReplacementsFinder<T> implements CommandVisitor<T> {
+
+  private List<T> pendingInsertions;
+  private List<T> pendingDeletions;
+  private int     skipped;
+
+  /** Handler to call when synchronized sequences are found. */
+  private ReplacementsHandler<T> handler;
+  
+  /** Simple constructor.
+   * Creates a new instance of ReplacementsFinder
+   * @param handler handler to call when synchronized sequences are
+   * found
+   */
+  public ReplacementsFinder(ReplacementsHandler<T> handler) {
+    pendingInsertions = new ArrayList<T>();
+    pendingDeletions  = new ArrayList<T>();
+    skipped           = 0;
+    this.handler      = handler;
+  }
+
+  /** Add an object to the pending insertions set.
+   * @param object object to insert
+   */
+  public void visitInsertCommand(T object) {
+    pendingInsertions.add(object);
+  }
+  
+  /** Handle a synchronization object.
+   * <p>When a synchronization object is identified, the pending
+   * insertions and pending deletions sets are provided to the user
+   * handler as subsequences.</p>
+   * @param object synchronization object detected
+   */
+  public void visitKeepCommand(T object) {
+    if (pendingDeletions.isEmpty() && pendingInsertions.isEmpty()) {
+      ++skipped;
+    } else {
+      handler.handleReplacement(skipped, pendingDeletions, pendingInsertions);
+      pendingDeletions.clear();
+      pendingInsertions.clear();
+      skipped = 1;
+    }
+  }
+  
+  /** Add an object to the pending deletions set.
+   * @param object object to delete
+   */
+  public void visitDeleteCommand(T object) {
+    pendingDeletions.add(object);
+  }
+
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsHandler.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsHandler.java?rev=1311904&view=auto
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsHandler.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/ReplacementsHandler.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+import java.util.List;
+
+/** This interface is devoted to handle synchronized replacement sequences.
+ * @see ReplacementsFinder
+ * @since 4.0
+ * @author Luc Maisonobe
+ * @version $Id$
+ */
+public interface ReplacementsHandler<T> {
+
+  /** Handle two synchronized sequences.
+   * <p>This method is called by a {@link ReplacementsFinder
+   * ReplacementsFinder} instance when it has synchronized two
+   * sub-sequences of object arrays being compared, and at least one
+   * of the sequences is non-empty. Since the sequences are
+   * synchronized, the objects before the two sub-sequences are equals
+   * (if they exist). This property also holds for the objects after the
+   * two sub-sequences.</p>
+   * <p>The replacement is defined as replacing the <code>from</code>
+   * sub-sequence into the <code>to</code> sub-sequence.</p>
+   * @param skipped number of tokens skipped since the last call (i.e.
+   * number of tokens that were in both sequences), this number should
+   * be strictly positive except on the very first call where it can be
+   * zero (if the first object of the two sequences are different)
+   * @param from sub-sequence of objects coming from the first sequence
+   * @param to sub-sequence of objects coming from the second sequence
+   */
+  public void handleReplacement(int skipped, List<T> from, List<T> to);
+
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/SequencesComparator.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/SequencesComparator.java?rev=1311904&view=auto
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/SequencesComparator.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/SequencesComparator.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,265 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+import java.util.List;
+
+
+/**
+
+ * This class allows to compare two objects sequences.
+
+ * <p>The two sequences can hold any object type, as only the
+ * <code>equals</code> method is used to compare the elements of the
+ * sequences. It is guaranteed that the comparisons will always be
+ * done as <code>o1.equals(o2)</code> where <code>o1</code> belongs to
+ * the first sequence and <code>o2</code> belongs to the second
+ * sequence. This can be important if subclassing is used for some
+ * elements in the first sequence and the <code>equals</code> method
+ * is specialized.</p>
+
+ * <p>Comparison can be seen from two points of view: either as
+ * giving the smallest modification allowing to transform the first
+ * sequence into the second one, or as giving the longest sequence
+ * which is a subsequence of both initial sequences. The
+ * <code>equals</code> method is used to compare objects, so any
+ * object can be put into sequences. Modifications include deleting,
+ * inserting or keeping one object, starting from the beginning of the
+ * first sequence.</p>
+
+ * <p>This class implements the comparison algorithm, which is the
+ * very efficient algorithm from Eugene W. Myers <a
+ * href="http://www.cis.upenn.edu/~bcpierce/courses/dd/papers/diff.ps">An
+ * O(ND) Difference Algorithm and Its Variations</a>. This algorithm
+ * produces the shortest possible {@link
+ * org.apache.commons.collections.list.difference.EditScript edit script}
+ * containing all the {@link
+ * org.apache.commons.collections.list.difference.EditCommand commands} needed to
+ * transform the first sequence into the second one.</p>
+
+ * @see EditScript
+ * @see EditCommand
+ * @see CommandVisitor
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @version $Id$
+ */
+public class SequencesComparator<T> {
+
+  /** First sequence. */
+  private List<T> sequence1;
+
+  /** Second sequence. */
+  private List<T> sequence2;
+
+  /** Temporary variables. */
+  private int[] vDown;
+  private int[] vUp;
+
+  /** Simple constructor.
+   * <p>Creates a new instance of SequencesComparator</p>
+   * <p>It is <em>guaranteed</em> that the comparisons will always be
+   * done as <code>o1.equals(o2)</code> where <code>o1</code> belongs
+   * to the first sequence and <code>o2</code> belongs to the second
+   * sequence. This can be important if subclassing is used for some
+   * elements in the first sequence and the <code>equals</code> method
+   * is specialized.</p>
+   * @param sequence1 first sequence to be compared
+   * @param sequence2 second sequence to be compared
+   */
+  public SequencesComparator(List<T> sequence1, List<T> sequence2) {
+    this.sequence1 = sequence1;
+    this.sequence2 = sequence2;
+
+    int size = sequence1.size() + sequence2.size() + 2;
+    vDown = new int[size];
+    vUp   = new int[size];
+
+  }
+
+  /** Build a snake.
+   * @param start the value of the start of the snake
+   * @param diag the value of the diagonal of the snake
+   * @param end1 the value of the end of the first sequence to be compared
+   * @param end2 the value of the end of the second sequence to be compared
+   * @return the snake built
+   */
+  private Snake buildSnake(int start, int diag, int end1, int end2) {
+    int end = start;
+    while (((end - diag) < end2)
+           && (end < end1)
+           && sequence1.get(end).equals(sequence2.get(end - diag))) {
+      ++end;
+    }
+    return new Snake(start, end, diag);
+  }
+
+  /** Get the middle snake corresponding to two subsequences of the
+   * main sequences.
+   * The snake is found using the MYERS Algorithm (this algorithms has
+   * also been implemented in the GNU diff program). This algorithm is
+   * explained in Eugene Myers article: <a
+   * href="http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps">An
+   * O(ND) Difference Algorithm and Its Variations</a>.
+   * @param start1 the begin of the first sequence to be compared
+   * @param end1 the end of the first sequence to be compared
+   * @param start2 the begin of the second sequence to be compared
+   * @param end2  the end of the second sequence to be compared
+   * @return the middle snake
+   */
+  private Snake getMiddleSnake(int start1, int end1, int start2, int end2) {
+    // Myers Algorithm
+    //Initialisations
+    int m = end1 - start1;
+    int n = end2 - start2;
+    if ((m == 0) || (n == 0)) {
+      return null;
+    }
+
+    int delta  = m - n;
+    int sum    = n + m;
+    int offset = ((sum % 2 == 0) ? sum : (sum + 1)) / 2;
+    vDown[1+offset] = start1;
+    vUp[1+offset]   = end1 + 1;
+
+    for (int d = 0; d <= offset ; ++d) {
+      // Down
+      for (int k = -d; k <= d; k += 2) {
+        // First step
+
+        int i = k + offset;
+        if ((k == -d) || ((k != d) && (vDown[i-1] < vDown[i+1]))) {
+          vDown[i] = vDown[i+1];
+        } else {
+          vDown[i] = vDown[i-1] + 1;
+        }
+
+        int x = vDown[i];
+        int y = x - start1 + start2 - k;
+
+        while ((x < end1) && (y < end2) && (sequence1.get(x).equals(sequence2.get(y)))) {
+          vDown[i] = ++x;
+          ++y;
+        }
+        // Second step
+        if (((delta % 2) != 0 ) && ((delta - d) <= k) && (k <= (delta + d))) {
+          if (vUp[i-delta] <= vDown[i]) {
+            return buildSnake(vUp[i-delta], k + start1 - start2, end1, end2);
+          }
+        }
+      }
+
+      // Up
+      for (int k = (delta - d); k <= (delta + d); k += 2) {
+        // First step
+        int i = k + offset - delta;
+        if ((k == (delta - d))
+            || ((k != (delta + d)) && (vUp[i+1] <= vUp[i-1]))) {
+          vUp[i] = vUp[i+1] - 1;
+        } else {
+          vUp[i] = vUp[i-1];
+        }
+
+        int x = vUp[i] - 1;
+        int y = x - start1 + start2 - k;
+        while ((x >= start1) && (y >= start2)
+               && sequence1.get(x).equals(sequence2.get(y))) {
+          vUp[i] = x--;
+          y--;
+        }
+        // Second step
+        if (((delta % 2) == 0) && (-d <= k) && (k <= d) ) {
+          if (vUp[i] <= vDown[i + delta]) {
+            return buildSnake(vUp[i], k + start1 - start2, end1, end2);
+          }
+        }
+      }
+    }
+
+    // this should not happen
+    throw new RuntimeException("Internal Error");
+
+  }
+
+
+  /** Build an edit script.
+   * @param start1 the begin of the first sequence to be compared
+   * @param end1 the end of the first sequence to be compared
+   * @param start2 the begin of the second sequence to be compared
+   * @param end2  the end of the second sequence to be compared
+   * @param script the edited script
+   */
+  private void buildScript(int start1, int end1, int start2, int end2,
+                           EditScript<T> script) {
+
+    Snake middle = getMiddleSnake(start1, end1, start2, end2);
+
+    if ((middle == null)
+    || ((middle.getStart() == end1) && (middle.getDiag() == (end1 - end2)))
+    || ((middle.getEnd() == start1) && (middle.getDiag() == (start1 - start2)))) {
+
+      int i = start1;
+      int j = start2;
+      while ((i < end1) || (j < end2)) {
+        if ((i < end1) && (j < end2) && sequence1.get(i).equals(sequence2.get(j))) {
+          script.append(new KeepCommand<T>(sequence1.get(i)));
+          ++i;
+          ++j;
+        } else {
+          if ((end1 - start1) > (end2 - start2)) {
+            script.append(new DeleteCommand<T>(sequence1.get(i)));
+            ++i;
+          } else {
+            script.append(new InsertCommand<T>(sequence2.get(j)));
+            ++j;
+          }
+        }
+      }
+
+    } else {
+
+      buildScript(start1, middle.getStart(),
+      start2, middle.getStart() - middle.getDiag(),
+      script);
+      for (int i = middle.getStart(); i < middle.getEnd(); ++i) {
+        script.append(new KeepCommand<T>(sequence1.get(i)));
+      }
+      buildScript(middle.getEnd(), end1,
+      middle.getEnd() - middle.getDiag(), end2,
+      script);
+    }
+  }
+
+  /** Get the edit script script.
+   * <p>It is guaranteed that the objects embedded in the {@link
+   * InsertCommand insert commands} come from the second sequence and
+   * that the objects embedded in either the {@link DeleteCommand
+   * delete commands} or {@link KeepCommand keep commands} come from
+   * the first sequence. This can be important if subclassing is used
+   * for some elements in the first sequence and the
+   * <code>equals</code> method is specialized.</p>
+   * @return the edit script resulting from the comparison of the two
+   * sequences
+   */
+  public EditScript<T> getScript() {
+    EditScript<T> script = new EditScript<T>();
+    buildScript(0, sequence1.size(), 0, sequence2.size(), script);
+    return script;
+  }
+
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/Snake.java
URL: http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/Snake.java?rev=1311904&view=auto
==============================================================================
--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/Snake.java (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/Snake.java Tue Apr 10 18:22:29 2012
@@ -0,0 +1,86 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.collections.list.difference;
+
+/**
+ * This class is a simple placeholder to hold the end part of a path
+ * under construction in a {@link SequencesComparator
+ * SequencesComparator}.
+
+ * <p>A snake is an internal structure used in Eugene W. Myers
+ * algorithm (<a
+ * href="http://www.cis.upenn.edu/~bcpierce/courses/dd/papers/diff.ps">An
+ * O(ND) Difference Algorithm and Its Variations</a>).</p>
+
+ * @since 4.0
+ * @author Jordane Sarda
+ * @version $Id$
+ */
+  public class Snake {
+
+   /** Start index. */
+   private int start;
+
+   /** End index. */
+   private int end;
+
+   /** Diagonal number. */
+   private int diag;
+   
+  /** Simple constructor.
+   * Creates a new instance of Snake with default indices
+   */
+   public Snake() {
+     start = -1;
+     end   = -1;
+     diag  =  0;
+   }
+
+   /** Simple constructor.
+   * Creates a new instance of Snake with specified indices
+   * @param start start index of the snake
+   * @param end end index of the snake
+   * @param diag diagonal number
+   */ 
+  public Snake(int start, int end, int diag) {
+    this.start = start;
+    this.end   = end;
+    this.diag  = diag;
+ }
+  
+  /** Get the start index of the snake.
+   * @return start index of the snake
+   */
+  public int getStart() {
+    return start;
+  }
+ 
+  /** Get the end index of the snake.
+   * @return end index of the snake
+   */
+  public int getEnd() {
+    return end;
+  }
+
+  /** Get the diagonal number of the snake.
+   * @return diagonal number of the snake
+   */  
+  public int getDiag() {
+    return diag;
+  }
+  
+}

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Added: commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/package.html
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--- commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/package.html (added)
+++ commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/list/difference/package.html Tue Apr 10 18:22:29 2012
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+<!-- $Id$ -->
+ <!--
+   Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You under the Apache License, Version 2.0
+  (the "License"); you may not use this file except in compliance with
+  the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+  -->
+<body>
+This package provides classes to compare two objects sequences.
+
+<p>
+The two sequences can hold any object type, as only the
+<code>equals</code> method is used to compare the elements of the
+sequences. It is guaranteed that the comparisons will always be done
+as <code>o1.equals(o2)</code> where <code>o1</code> belongs to the
+first sequence and <code>o2</code> belongs to the second
+sequence. This can be important if subclassing is used for some
+elements in the first sequence and the <code>equals</code> method is
+specialized.
+</p>
+
+<p>
+Comparison can be seen from two points of view: either as giving the
+smallest modification allowing to transform the first sequence into
+the second one, or as giving the longest sequence which is a
+subsequence of both initial sequences. The <code>equals</code> method
+is used to compare objects, so any object can be put into
+sequences. Modifications include deleting, inserting or keeping one
+object, starting from the beginning of the first sequence. Like most
+algorithms of the same type, objects transpositions are not
+supported. This means that if a sequence <code>(A, B)</code> is
+compared to <code>(B, A)</code>, the result will be either the
+sequence of three commands <code>delete A</code>, <code>keep B</code>,
+<code>insert A</code> or the sequence  <code>insert B</code>,
+<code>keep A</code>, <code>delete B</code>.
+</p>
+
+<p>
+The package uses a very efficient comparison algorithm designed by
+Eugene W. Myers and described in his paper: <a
+href="http://www.cis.upenn.edu/~bcpierce/courses/dd/papers/diff.ps">An O(ND)
+Difference Algorithm and Its Variations</a>. This algorithm produces
+the shortest possible {@link
+org.apache.commons.collections.list.difference.EditScript edit script} containing
+all the {@link org.apache.commons.collections.list.difference.EditCommand
+commands} needed to transform the first sequence into the second
+one. The entry point for the user to this algorithm is the {@link
+org.apache.commons.collections.list.difference.SequencesComparator
+SequencesComparator} class.
+</p>
+
+<p>
+As explained in Gene Myers paper, the edit script is equivalent to all
+other representations and contains all the needed information either
+to perform the transformation, of course, or to retrieve the longest
+common subsequence for example.
+</p>
+
+<p>
+If the user needs a very fine grained access to the comparison result,
+he needs to go through this script by providing a visitor implementing
+the {@link org.apache.commons.collections.list.difference.CommandVisitor
+CommandVisitor} interface.
+</p>
+
+<p>
+Sometimes however, a more synthetic approach is needed. If the user
+prefers to see the differences between the two sequences as global
+<code>replacement</code> operations acting on complete subsequences of
+the original sequences, he will provide an object implementing the
+simple {@link org.apache.commons.collections.list.difference.ReplacementsHandler
+ReplacementsHandler} interface, using an instance of the {@link
+org.apache.commons.collections.list.difference.ReplacementsFinder
+ReplacementsFinder} class as a command converting layer between his
+object and the edit script. The number of objects which are common to
+both initial arrays and hence are skipped between each call to the user
+{@link
+org.apache.commons.collections.list.difference.ReplacementsHandler#handleReplacement
+handleReplacement} method is also provided. This allows the user to keep
+track of the current index in both arrays if he needs so.
+</p>
+
+</body>

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