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IllegalArgumentException for own Listener class [message #459949]

Sat, 20 August 2005 15:33

Eclipse User

Originally posted by: murley.murley.murley

I have a combo box in my application. If i add listener like this, it works
fine:
Combo c = new xxxxx;
c.addListener(SWT.Selection, new Listener(){
public void handleEvent(Event evt){
System.out.println("selection ...");
}
});

I create my own class "MyListener":
public class MyListener implements Listener{
public void handleEvent(Event event){
System.out.println("MyListener ..");
}
}
then if i add listener like this:
MyListener myLis;
c.addListener(SWT.Selection, myLis);

Then java.lang.IllegalArgumentException occur.
Do anyone know what mistake i make?
I have no idea in it...
Thanks

Re: IllegalArgumentException for own Listener class [message #459957 is a reply to message #459949]

Sun, 21 August 2005 13:16

Eclipse User

murley wrote:
> I have a combo box in my application. If i add listener like this, it works
> fine:
> Combo c = new xxxxx;
> c.addListener(SWT.Selection, new Listener(){
> public void handleEvent(Event evt){
> System.out.println("selection ...");
> }
> });
>
> I create my own class "MyListener":
> public class MyListener implements Listener{
> public void handleEvent(Event event){
> System.out.println("MyListener ..");
> }
> }
> then if i add listener like this:
> MyListener myLis;
> c.addListener(SWT.Selection, myLis);
>
> Then java.lang.IllegalArgumentException occur.
> Do anyone know what mistake i make?
> I have no idea in it...
> Thanks
>
>

Are you sure you wrote:

MyListener myLis;

and not

MyListener myLis = new MyListener();

cause then you probably have a null pointer exception.

- Johan

Re: IllegalArgumentException for own Listener class [message #459958 is a reply to message #459957]

Sun, 21 August 2005 13:45

Eclipse User

Originally posted by: murley.murley.murley

Oh, i forgot to instantiate ...
B.T.W why the error is "IllegalArgumentException" but not
"NullPointerException"

Re: IllegalArgumentException for own Listener class [message #460076 is a reply to message #459958]

Mon, 22 August 2005 00:44

Eclipse User

murley wrote:
> Oh, i forgot to instantiate ...
> B.T.W why the error is "IllegalArgumentException" but not
> "NullPointerException"
>
>

Because the method checks it's arguments instead of letting the null
pointer be dereferenced:

if (arg == null)
throw new ...

Re: IllegalArgumentException for own Listener class [message #460086 is a reply to message #460076]

Mon, 22 August 2005 06:38

Eclipse User

Originally posted by: murley.murley.murley

i got it, thanks for reply~

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