How can that possible compile???

[David Lopes]

This compiles:

public <T extends Integer> T aMethod(){
       return 35;
}

This one does not compile:

public <T extends Integer> T aMethod(){
       return new Integer(35);
}

I know that Integer is final and can't be extended, that is why the second example won't compile. But how is possible that the first example compiles and actually returns 35?

In Brazilian forums, there are some guys saying that could even be a Compiler Error, I doubt that but I haven't found any explanation.

Thanks for the Help.

[Duc Vo]

I would guess it works because of autoboxing feature. Autoboxing only means for the compiler to treat value type as reference type, properly in your case it will be treated as T.

Also, with the second code block if you cast the return result to T then it can be compiled.

public <T extends Integer> T aMethod() {
	return (T) new Integer(35);
}

[Punit Singh]

I am compiling from the command line and your both examples are not compiling.
Try to run them from command line.

[Sunny Mattas]

hi
For me also both examples are not compiling.
And i think it has nothing to do with Integer class because following code is also not compiling.

class St1
 {

    public <T extends St1> T aMethod(){
             return new St1();
         }

 }

St1.java:7: incompatible types
found   : St1
required: T
        return new St1();
               ^

But this is compiling with a warning

class St1
 {



public <T extends St1> T aMethod(){
        return (T)new St1();
 }

 }

[Duc Vo]

Well I compile it with eclipse 3.4. Not sure what compiler options that eclipse is using.

[David Lopes]

Punit Singh wrote:I am compiling from the command line and your both examples are not compiling.
Try to run them from command line.

In fact, when compiling from command line (javac) the first example won't compile as well.

The strange is that my Eclipse uses the jdk 1.6 located at the same directory but of course it uses the javaw.exe to compile, not the javac.

Is there anything wrong with the javaw.exe ? oO

[Punit Singh]

David Lopes wrote:

Punit Singh wrote:I am compiling from the command line and your both examples are not compiling.
Try to run them from command line.

In fact, when compiling from command line (javac) the first example won't compile as well.

The strange is that my Eclipse uses the jdk 1.6 located at the same directory but of course it uses the javaw.exe to compile, not the javac.

Is there anything wrong with the javaw.exe ? oO

This is not the first issue with eclipse, you will lots of these type of issues in future as I have got too many, so be careful, do not depend on eclipse.

[Punit Singh]

One more example I remember is this one:
Here this is allowed in eclipse, but it is compile time error on command line.

  Integer iii=(short)4;//allowed in eclipse but not on command line.
        Integer i4=(char)4;
        Integer i5=(byte)4;  

[David Lopes]

Contacted Eclipse Foundation,

They confirmed the bug and it will be corrected at the next patch.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=264843

[Ruben Soto]

I thought Eclipse didn't change core java and javac behavior. I thought of it as a giant GUI wrapper with added functionality. This is interesting, is Eclipse preparsing the code somehow? And for what reason?

[Jesper de Jong]

Eclipse does not use javac - it has its own built-in Java compiler, based on IBM's Jikes Java compiler. (Eclipse was originally created by IBM).

Eclipse is ofcourse supposed to work the same way as Sun's Java compiler. If it doesn't, it's a bug in Eclipse.

[Ruben Soto]

That explains things, thanks for clarifying that, Jesper.