Inner class method call

[d915172]

interface I {
  void ishow();
}

public class An {
  I getI() {
    return new I() {
      public void ishow() { }
      void print() { } //(*) // how can we access this method?
    };
  }
  public static void main(String[] args) {
    (new An()).getI().ishow();
    // ! (new An()).getI()).print(); - obviously won't work (compilation error)
  }
}

How can we access a anonymous inner class method or field* that is not described in interface? or is it possible without adding the method to the interface?

*I guess only static final fields are valid inside an interface body

[pbrockway2]

Since An declares getI() to return an instance of I, the compiler will wisely forbid you to do anything with that instance other than what an I promises to be able to do.

You could have another class (or interface) AnI which implements (or extends) I and has the print() method. getI() could be declared to return an instance of AnI. The important thing is that the caller of getI() - which could be someone else's code in some other totally unrelated package written years later (*) - has a publically exposed API, such as that provided by AnI, to work to.

Edit: * OK, getI() has only default accessibility, but the point remains.

[StormyWaters]

You can but its tricky and ugly.

public interface Interface {
	public void show();	
}



public class Test {
	
	public Interface getInterface() {
		return new Interface(){
			public void show() {
				System.out.println("Show");				
			}
			public void print() {
				System.out.println("print");
			}
		};
	}
	
	public static void main(String[] args) {
		Test test = new Test();
		Interface inter = test.getInterface();
		inter.show();
		
		try {
			inter.getClass().getMethod("print", new Class[]{}).invoke(inter, new Object[]{});
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		}
	}
}

It would be a better approach to either create a class that implements the interface and provides the extra method, or create a new interface which extends the current interface and add the method to the new interface.

public class InterfaceObject implements Interface {

	public void show() {
		System.out.println("Show");
	}
	
	public void print() {
		System.out.println("Print");
	}
}

public interface SubInterface extends Interface {
	public void print();
}

[d915172]

StormyWaters, I checked your code, it works perfect (just needed to add one import) and answers my question!

Thanks a lot!