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From "Sergei Ivanov (JIRA)" <j...@apache.org>
Subject [jira] Created: (LANG-536) Add isSorted() to ArrayUtils
Date Thu, 24 Sep 2009 16:43:16 GMT
Add isSorted() to ArrayUtils
----------------------------

                 Key: LANG-536
                 URL: https://issues.apache.org/jira/browse/LANG-536
             Project: Commons Lang
          Issue Type: New Feature
            Reporter: Sergei Ivanov
            Priority: Minor


In my unit tests I often need to verify that an array is correctly sorted.
In order to achieve this, I've got two helper methods as follows.
Is it possible to integrate these methods into ArrayUtils?

{code}

    /**
     * Checks that the specified array of objects is in an ascending order
     * according to the specified comparator.  All elements in the array must be
     * <i>mutually comparable</i> by the specified comparator (that is,
     * <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
     * for any elements <tt>e1</tt> and <tt>e2</tt> in the array).
     *
     * @param a the array to be checked.
     * @param c the comparator to determine the order of the array.  A
     * <tt>null</tt> value indicates that the elements'
     * {@linkplain Comparable natural ordering} should be used.
     * @return {@code true}, if the array is sorted; {@code false}, otherwise.
     * @throws ClassCastException if the array contains elements that are
     * not <i>mutually comparable</i> using the specified comparator.
     */
    public static <T> boolean isSorted(final T[] a, final Comparator<? super T>
c) {
        if (a.length <= 1) {
            // Empty or singleton arrays are always sorted
            return true;
        }
        // Otherwise, check that every element is not smaller than the previous
        T previous = a[0];
        for (int i = 1, n = a.length; i < n; i++) {
            final T current = a[i];
            if (c.compare(previous, current) > 0) {
                return false;
            }
            previous = current;
        }
        return true;
    }

    /**
     * Checks that the specified array of objects is in an ascending order,
     * according to the {@linkplain Comparable natural ordering} of its elements.
     * All elements in the array must implement the {@link Comparable} interface.
     * Furthermore, all elements in the array must be <i>mutually comparable</i>
     * (that is, <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
     * for any elements <tt>e1</tt> and <tt>e2</tt> in the array).
     *
     * @param a the array to be checked.
     * @return {@code true}, if the array is sorted; {@code false}, otherwise.
     * @throws ClassCastException if the array contains elements that are not
     * <i>mutually comparable</i> (for example, strings and integers).
     */
    @SuppressWarnings({"unchecked"})
    public static <T> boolean isSorted(final T[] a) {
        if (a.length <= 1) {
            // Empty or singleton arrays are always sorted
            return true;
        }
        // Otherwise, check that every element is not smaller than the previous
        T previous = a[0];
        for (int i = 1, n = a.length; i < n; i++) {
            final T current = a[i];
            if (((Comparable<? super T>) previous).compareTo(previous) > 0) {
                return false;
            }
            previous = current;
        }
        return true;
    }

{code}

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