Re: [platform-dev] generics: different behaviour between Eclipse 3.2 and

[John Arthorne <John_Arthorne@xxxxxxxxxx>]

Please enter a bug report in Eclipse
bugzilla against JDT core.
John

Bojan Antonovic <bojan@xxxxxxxxxxxxx>
Sent by: platform-dev-bounces@xxxxxxxxxxx

22/07/2006 07:35 PM

Please respond to
"Eclipse platform general developers list." <platform-dev@xxxxxxxxxxx>

To	platform-dev@xxxxxxxxxxx
cc
Subject	[platform-dev] generics: different behaviour between Eclipse 3.2        and Sun's javac

I have the problem that Eclipse 3.2 and Sun's javac
behave differently 
for Java generics. Eclipse accepts more, or Sun's javac (up to Java 6 
Beta 2) is more strict, or one of them is buggy.

Example 1:
 
    public <T> Class<? extends T> fooGetClass(final
T object) {
        return object.getClass();
    }

Eclipse reports no warnings. javac says:

smood/GetClassTest.java:6: incompatible types
found   : java.lang.Class<capture of ? extends java.lang.Object>
required: java.lang.Class<? extends T>
                return object.getClass();

I think I've read that this is an exception in the JLS, which Eclipse 
supports correctly, but I'm not sure. If I use a cast

    public <T> Class<? extends T> fooGetClass(final
T object) {
        return (Class<? extends T>) object.getClass();
    }
   
javac doesn't complain (it compiles the code), but Eclipse reports a 
necessary cast.

Example 2:

public static <T extends Comparable<T>> T 
readComparableParameter(ComparableParameter<T> parameter {
    // some code
}

using it in

        for (ComparableParameter<? extends Comparable<?>>
parameter: 
parameterSet)
        {
           readComparableParameter(parameter);
        }

leads to a pattern matching problem in javac.

I have many of things strange behaviours, specially when using wildcards.

I'm using Java generics since more than 1 year, but still I have 
sometimes problems. Mostly with erasure. BTW, who invented the bullshit
that

    ArrayList<Object> x=new ArrayList<String>();

doesn't work but

    ArrayList<? extends Object> x=new ArrayList<String>();

does? This distinction is absolut useless, and against all OOP 
principles! It just enforces you to write "? extends" everywhere!

Or that the wildcard is sometimes higher that Object!

Why can't I have the class of Map as Class<Map<?,?>>, but only
Class<Map>, even if I can't have Class<Map<K,V>> because
of erasure? How 
can I avoid raw types, as there's a new warning in Eclipse 3.2, when 
this doesn't work. But you can create:

Map<?,?>[] mapArray=new Map<?,?>[5];

Sorry for mixing but reports with design problems and listening to my 
frustrations. But I'm sometimes forced to go back to raw types as I 
can't figure out how to use generics. Transforming a project of 40'000
LOC in Java to Java 5 is more complicated if you have strange 
restrictions. Or bugs like 
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6218229.

greetings

    Bojan

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