About Question enthuware.ocpjp.v7.2.1369 :

[Wisevolk]

Hi, So the only way to use doA(0 declare in the anonymous class is to use it whitin that declaration ?

[admin]

Not sure what you mean. Can you please put what you mean in code?
-Paul.

[Wisevolk]

in your code the method declare at //2 can only be use in the scope of the new inner() declaration at //1 because it's an anonymous class ?
package test;
public class TopClass {
public Inner inner1 = new Inner() //1
{
        public void doA(){  // 2
System.out.println("doing A");
}     
};
public void doA() { inner1.doA(); }
}
class Inner {    int value; }

[admin]

Yes, but not just because it is an anonymous inner class. It is also because the declaration of doA() is not present in class Inner. So you cannot call doA() on a variable of type Inner.

It is really same as introducing a new method in a sub class. For example, if you have two classes InputDevice and KeyBoard, where KeyBoard extends InputDevice and KeyBoard has an extra method getNumberOfKeys(), you can't call this method on a variable of class InputDevice. i.e.

InputDevice id = new KeyBoard() ; //This is fine
id.getNumberOfKeys(); //This will not compile.

Of course, within the KeyBoard class, you can call getNumberOfKeys() on 'this'.

HTH,
Paul.

[Wisevolk]

Thnks

[vijayanand]

Does this mean that the anonymous inner class inner1 is like extending class Inner with its doA() method ?

[admin]

Yes, that is correct.

[vijayanand]

What i understand is anonymous inner class can be created only in a code block (inside method, constructor, or intialization block).

How does compiler allows creating anonymous inner class inside top-level class?

[admin]

Sorry, I don't understand your question.

[jagoneye]

Also note guys non-overrided methods inside anonymous class can be called!
It can be done by placing the call inside the overrided method.

Code: Select all

class InnerTest1
{
 public static void main(String args[])
   {
InnerTest1 i1 = new InnerTest1(){
          public void callme()
          {
              m1();
          }
          void m1(){
              System.out.println("m1");
          }
      };
      i1.callme();
   }
public void callme()
   {
   }
}

I think this should also be added to the explaination if it is worth it!

[Harvey Manfrenjensen]

>>>Observe that there is no way doA() can be accessed.
fyi...

Code: Select all

class TopClass
{
    public Inner inner1 = new Inner()
    {
        public Inner doA(){  
            System.out.println("doing A"); 
            return this;
        }
    }.doA();  // call doA() here

    public void doA() { inner1.doA(); }
}

class Inner
{
   int value;
}

[admin]

Assuming that you are trying to show a counter example, have you even tried to compile your code?

[Harvey Manfrenjensen]

you are right, it does not compile, i took it from the explanation of question,
which show inappropriate call of a new method of anonymous class.
Here is example, that compiles.

Regards, Paul

Code: Select all

class TopClass
{
    public Inner inner1 = new Inner()
    {
        public Inner doA(){  
            System.out.println("doing A"); 
            return this;
        }
    }.doA();  // call doA() here
}

class Inner
{
   int value;
}

[admin]

Yes, this compiles but this is not the doA() that is given in the problem statement.

Your code does show an interesting way to invoke a method of an inner class though.

regards,
Paul.