Comments on: Java Quiz of The Day – same private field instance for two classes

By: marko schulz

marko schulz — Tue, 02 Dec 2008 12:44:58 +0000

The idea of using a method private class is sweet and can be shortend by a few more characters, if you use an int instead of an object:

class MyClass {int ocl;} in the beginning of main() does the trick.

By: Ahti

Ahti — Tue, 02 Dec 2008 09:24:17 +0000

shamaz,

“private static final Object ocl = new Object();”

is not correct because you are allowed to change ONLY main method.

By: Christoph

Christoph — Tue, 02 Dec 2008 08:35:43 +0000

I’ll give it a try…

public class InstanceDemo {

public static void main(String[] args){
MyClass cl1 = new MyClass();
MyClass cl2 = (MyClass) cl1.clone();
System.out.println(cl1.ocl==cl2.ocl && cl1!=cl2);
}

private static class MyClass extends java.util.ArrayList {
private final Object ocl = new Object();
}
}

By: shamaz

shamaz — Tue, 02 Dec 2008 08:32:15 +0000

private static final Object ocl = new Object();

not that hard compared to some SCJP questions

By: Andreas Groll, Michael FÃ¼rstenberg

Andreas Groll, Michael FÃ¼rstenberg — Tue, 02 Dec 2008 08:20:53 +0000

public class InstanceDemo {

public static void main(final String[] args) {
MyClass cl1 = new MyClass();
MyClass cl2 = (MyClass)cl1.clone();
System.out.println(cl1.ocl == cl2.ocl && cl1 != cl2);
}

private static class MyClass extends java.util.ArrayList {
private final Object ocl = new Object();
}

}

By: Yuri Schimke

Yuri Schimke — Tue, 02 Dec 2008 06:11:39 +0000

MyClass cl2 = (MyClass) cl1.clone();

By: Patrick

Patrick — Tue, 02 Dec 2008 04:57:07 +0000

public static void main(String[] args) throws Exception { MyClass cl1 = new MyClass(); MyClass cl2 = new MyClass();


Field field = cl1.getClass().getDeclaredField("ocl");

field.setAccessible(true);

field.set(cl2,cl1.ocl);

System.out.println(cl1.ocl == cl2.ocl && cl1 != cl2); }

By: Brendan Bates

Brendan Bates — Tue, 02 Dec 2008 04:44:25 +0000

Change “MyClass cl2 = new MyClass();” to:

MyClass cl2 = (MyClass)cl1.clone();

By: Alex Smirnoff

Alex Smirnoff — Tue, 02 Dec 2008 00:24:27 +0000

Changing to

MyClass cl2 = (MyClass)cl1.clone();

Should make a trick. Can you publish the statistics about this question? Just wondering.

Thanks,
Alex.

By: Stephen Egan

Stephen Egan — Mon, 01 Dec 2008 23:52:48 +0000

public class InstanceDemo {

public static void main(String[] args) {
MyClass cl1 = new MyClass();
MyClass cl2 = (MyClass)(cl1.clone());
System.out.println(cl1.ocl == cl2.ocl && cl1 != cl2);
}

private static class MyClass extends java.util.ArrayList {
private final Object ocl = new Object();
}

}