如何从另一个类调用抽象内部类的方法？

Question

public class OuterClass {
     abstract class InnerClass {
         int value = 20;
         public void print(){
                 System.put.println("Value = " + getValue());
         }
         public abstract int getValue();
      }
 }

Can someone help me, how do I call the method print() from another Java class that has the main method?

Answer 1

You can't instantiate an abstract class, so to call an instance method of that class you need to subclass it.

In order to subclass it you need to implement its abstract methods.

new OuterClass().new InnerClass()
{
   public int getValue()
   {
      return 1;
   }
}.print();

Is one way to do it, although in practice you would probably want to do this differently, one way would be as JBNizet suggests to have a method in OuterClass to return the type of InnerClass that you want.

Answer 2

Since InnerClass is non static you need an instance of OuterClass to access it. Next since it is abstract class you need a subclass whose instance you can actually create. From the subclass you can call the super classes method using super.

One way I can think of is

public class HelloWorld {


    public static void main(String args[]) {

        OuterClass outerClass = new OuterClass();
        InnerSubClass myInstance = outerClass.new InnerSubClass();
        myInstance.print();
    }
}

class OuterClass {

    private InnerSubClass myInstance;

    abstract class InnerClass {
        int value = 20;
        public void print(){
                System.out.println("Value = " + getValue());
        }
        public abstract int getValue();
     }

    class InnerSubClass extends InnerClass{

        @Override
        public void print(){
            super.print();
            System.out.println("In SUbclass");
        }

        @Override
        public int getValue() {
            return 0;
        }

    }
}