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From "Piyush Purang (JIRA)" <j...@apache.org>
Subject [jira] Created: (JCR-320) BinaryValue equals fails for two objects with two different byte arrays that contain the same bytes.
Date Wed, 15 Feb 2006 18:39:11 GMT
BinaryValue equals fails for two objects with two different byte arrays that contain the same
bytes.
----------------------------------------------------------------------------------------------------

         Key: JCR-320
         URL: http://issues.apache.org/jira/browse/JCR-320
     Project: Jackrabbit
        Type: Bug
  Components: core  
    Versions: 0.9    
    Reporter: Piyush Purang
    Priority: Minor


http://svn.apache.org/repos/asf/incubator/jackrabbit/trunk/jackrabbit/src/main/java/org/apache/jackrabbit/value/BinaryValue.java


Here is the present implementation

    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof BinaryValue) {
            BinaryValue other = (BinaryValue) obj;
            if (text == other.text && stream == other.stream
                    && streamData == other.streamData) {
                return true;
            }
            // stream, streamData and text are mutually exclusive,
            // i.e. only one of them can be non-null
            if (stream != null) {
                return stream.equals(other.stream);
            } else if (streamData != null) {
                return streamData.equals(other.streamData);
            } else {
                return text.equals(other.text);
            }
        }
        return false;
    }


Here are the problems with the present implementation


1. streamData.equals(other.streamData ) will fail miserably.

2. too many return statements! I guess no one ran a checkstyle on it.

3. return stream.equals(other.stream); will always be false unless both have been created
with the same InputStream!  

I wrote some testcases in SetValueBinaryTest

    public void testBinaryValueEquals() throws Exception {
        BinaryValue binaryValue1 = null;
        BinaryValue binaryValue2 = null;

        // initialize some binary value
        data = createRandomString(10).getBytes();
        binaryValue1 = (BinaryValue) superuser.getValueFactory().createValue(new ByteArrayInputStream(data));
        binaryValue2 = (BinaryValue) superuser.getValueFactory ().createValue(new ByteArrayInputStream(data));
        //ideallly setup a test harness that tests all the cases as defined by the contract
in Object.equals()
        assertTrue( binaryValue1.equals(binaryValue2));
        assertTrue( binaryValue1.equals(binaryValue1));
        assertFalse( binaryValue1.equals(null));
    }


    public void testBinaryValueEquals2() throws Exception {
        String str = createRandomString(10);
        BinaryValue binaryValue1 = new BinaryValue(str.getBytes());
        BinaryValue binaryValue2 = new BinaryValue(str.getBytes());

        assertTrue( binaryValue1.equals(binaryValue2));
        assertTrue( binaryValue1.equals(binaryValue1));
        assertFalse( binaryValue1.equals(null));
    }
    
    public void testBinaryValueEquals3() throws Exception {
        String str1 = "Some string xyz";
        String str2 = new StringBuffer().append("Some string xyz").toString();
        BinaryValue binaryValue1 = new BinaryValue(str1);
        BinaryValue binaryValue2 = new BinaryValue(str2);

        assertTrue( binaryValue1.equals(binaryValue2));
        assertTrue( binaryValue1.equals(binaryValue1));
        assertFalse( binaryValue1.equals(null));
    }


They were written quickly but with the present implementation the first two fail at the very
first assert* statement which for stream I can understand (as we are basically propogating
InputStream's equals contract) but for byte arrays I can't agree with this behaviour unless
it is so intended. It behaves the best when BinaryVlaue wraps a string i.e. testBinaryValueEquals3()
 passes without trouble.

I propose a new implementation where I am not very convinced with the behaviour when we have
streams being wrapped. If it should fail for the streams then we should change the documentation
for the method. As for making it work right when streams are involved .. well the streams
will have to be read and compared.

 
public boolean equals(Object obj) {
        boolean result = false;
        if (this == obj) {
            result = true;
        } else if (obj instanceof BinaryValue) {
            BinaryValue other = (BinaryValue) obj;
            // only one of text, stream and streamData are set at any given point
            if (text != null) {
                result = text.equals(other.text);
            } else if (stream != null) {
                result = stream.equals(other.stream);
            } else if (streamData != null) {
                result = Arrays.equals(streamData, other.streamData);
            } else {
                // all values are null; test that the other object (which could be us)
                // also has everything set to null!
                result = (other.text == null && other.stream == null
                        && other.streamData == null);
            }
        }
        return result;
    }

This implementation of course fails at the first assert* of the first test method testBinaryValueEquals
(It will pass the other two assert*s).

And if this new implementation doesn't fit the bill and an alternative isn't needed then just
skip implementing equals.

One more thought running through my mind is - if text, stream and data are mutually exclusive
why don't we have different classes for each of them? (Try and wrap a stringValue into a binary
value...)

I have also noticed that the hashCodes all return 0's throughtout the package. In the case
that the hashCode can't keep up with the contract of equal I would propose throwing an UnsupportedOpertaionException.
And if not then declare it in the BasValue as it will be inherited (unless this leads the
QA tools to report infringement of the rule that when you define equals you need to redefine
hashCode - checkstyle does that).

The value package doesn't have any tests for it.. or did I miss them? 

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