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From "Piyush Purang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-320) BinaryValue equals fails for two objects with two different byte arrays that contain the same bytes.
Date Thu, 16 Feb 2006 20:44:09 GMT
    [ http://issues.apache.org/jira/browse/JCR-320?page=comments#action_12366678 ] 

Piyush Purang commented on JCR-320:
-----------------------------------

Marcel you are spot on I erred there in my comment. What I wanted to say was returning different
int values would have signaled different types of values.. I actually got carried away there
:)

> No, we can't. :-) The JCR API explicitly says that Value.equals() must be implemented
in a specific way. See the javadoc link for details.

You are right Jukka, I forgot jackrabbit 0.9 doesn't mean that  the JCR API which is already
1.0 is still negotiable... :) and thanks for that discussion/mailing-list-archive link says
a lot. So I guess I should stop throwing the hashCode issue around?

Here are some fresh comments on this issue

1. I have started a new package org.apache.jackrabbit.test.api.value with a TestAll and other
classes. I hope that is fine.

2. Is there a way of getting the default encoding i.e. BaseValue.DEFAULT_ENCODING? and even
more importantly is there a way of setting a Default_Encoding conveniently through out the
repository for example what if a project wants to use UTF16 instead of UTF8 ? Has a thought
been put into that? Perhaps a config property? 

3. I have read the javadoc for Value (The third time mind you). Here are a few cases (to see
if I got it right)

a) two Binary Value with texts "some text" according to api they should be equal and by implementation
they are.
b) two Binary Values with bytes from "some text" in the same encoding according to api should
be equal(?) and with the implementation I proposed they are equal. 
what should happen if they have different encodings but the same content? I guess equals should
fail.
c) two BinaryValues with input streams from the same file will fail equals if the input streams
were instantiated independently. The javadoc asks not to try and compare big blobs so we stick
to that.

But what happens when one BinaryValue has text = "some text" and another a byte array = "some
text".getBytes(DEFAULT_ENCODING)?

and what happens when one BinaryValue has text = "some text" and another a stream from a file
with the contents "some text"?

If we decide that a BV with text="some text" must equal a BV  with byte array = "some text".getBytes(DEFAULT_ENCODING)
etc. etc. then I need to know now as the present equals implementation and my proposed one
fall way short!  We also need to write more tests then.. many more 

Next question: do we really need such a complex equals method i.e. do the other parts of the
API really care?

Another thought - we could simplify things if we didn't have a string in there and just have
a byte-array or a stream... as we can always re/create the string from the byte-array.

I hope no one's going to say ... seeesh leave it alone  it's just an equals method! ;)



> 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
>      Fix For: 1.0

>
> 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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