question about anonymous class

[josie chen]

according to JLS, instance initializers in anonymous class can throw any exception.
I don't know if my imagination of those code is correct or not. Since all I try cause compile error.
this is my testing code:
class AnonyExcptTest{
public void test() {
new AnonyExcptTest(){
{
// I suppose to add exception here.
throw new Exception();
}
public void mytest() throws Exception{
throw new Exception();
}
};
}
}
Who can help me to figure out?
Thanks a lot!
[e-mail]
[ April 02, 2003: Message edited by: josie chen ]

[William Barnes]

Don't know if this has anything to do with your question but you doing a "new" without assigning the result to anything.

[josie chen]

sorry, maybe my testing code is incorrect. could you give me an example to explain 'instance initializers in anonymous class can throw any exception.'
thank you very much.

[Jim Yingst]

public class AnonInstanceInit
{
  public static void main(String[] args) throws Exception
  {
    Runnable r = new Runnable()
        {
          {
            // make this "conditional" to fool compiler into thinking exception might not be thrown
            if (true)
              throw new Exception("foo");
          }
          public void run()
          {
            System.out.println("You'll never see this");
          }
        };
    new Thread(r).start();
  }
}

So, why does the language allow this? Well, let's say you're writing a class, and need the option to throw an exception during object construction. If the class is anonymous, you can't declara a new constructor for it - the only way you can throw an exception during initialization is in an instance initializer (or field initializer, which is pretty similar). Normally in order to throw a checked exception in an initializer, you'd be required to declare all constructors of your class so that they'd declare the new checked exception. But for an anonymous class, this is impossible - no way to declare constructors at all. This is OK since there's no way for anyone to invoke a constructor of your anonymous class anyway, except by calling the code that declares it, which must either catch the exception or declare it. (Note my main() method declares it throws Exception.) Any other code that calls your code will know about the checked exception, even though no constructor was declared to throw it.

[josie chen]

Very appreciate you, Jim.
The explaination is very clear.
I think I shoudn't rely on develper tool too much. Cause the results are different.