Java Anonymous Inner Class Calling Static Method

Question

I have the following code in an eclipse application:

import org.eclipse.swt.widgets.Listener; public class X { public void test() { Listener eclipseListener = new Listener() { public void handleEvent(Event evt) { System.err.println("starting"); Y.externalMethod(); System.err.println("finished"); } } } public class Y { public static void externalMethod() { System.err.println("in class Y"); } }

When I run method test in class X, I get the following output:

starting

I don't understand why externalMethod didn't run in class Y and why control didn't return to class X (it never prints 'finished' or 'in class Y').

Any ideas about why externalMethod doesn't run? Are anonymous inner classes not permitted to call static methods outside their class? If so, why does this code compile?

What you've posted works fine if you just add eclipseListener.handleEvent(null); and run it. Can you generate an SCCE? May well find the actual problem in the process. — Affe
– Affe, Commented Feb 4, 2013 at 22:34

Miserable Variable · Accepted Answer · 2013-02-04 22:41:42Z

1

Instead of

 public void handleEvent(Event evt) { System.err.println("starting"); Y.externalMethod(); System.err.println("finished"); }

you might have better luck with:

 public void handleEvent(Event evt) { System.err.println("starting handleEvent"); try { Y.externalMethod(); } finally { System.err.println("finished handleEvent"); } }

That is,

Put the method exit trace in finally
Add method names to trace lines

answered Feb 4, 2013 at 22:41

Miserable Variable

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4 Comments

David Over a year ago

Very interesting idea. When I tried it, the code in the finally branch does execute. I also tried adding a catch Exception e around the externalMethod, but it didn't catch anything.

Miserable Variable Over a year ago

Then you need to do the same thing with external method. Maybe it is throwing a RuntimeException or Error?

David Over a year ago

When I added a try/catch/finally around the code in Y.externalMethod, none of them printed (not the code in the catch or the finally method).

Miserable Variable Over a year ago

you mean the entry to method was printed but the exit was not? maybe it got a jvm error? that's unusual though. can you post its code or debug?

Eng.Fouad · Accepted Answer · 2013-02-04 22:31:26Z

0

The method handleEvent() is not invoked here. What you did is defining anonymous class and create an instance from it on the fly.

You need to register this listener (eclipseListener) to some event handler which will invoke the method handleEvent() when an event fires.

answered Feb 4, 2013 at 22:31

Eng.Fouad

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1 Comment

David Over a year ago

This is actually inside a much larger eclipse plugin event handler. The handleEvent method is executed when the listener is executed by clicking a button. When I execute the method, I get all debug lines until I call the static method in the external class. The static method in the external class has no parameters and it's first line is a debug message which does not print.

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