Chapter: Inner Classes

Create an interface U with three methods. Create a class A with a method that produces a reference to a U by building an anonymous inner class. Create a second class B that contains an array of U. B should have one method that accepts and stores a reference to a U in the array, a second method that sets a reference in the array (specified by the method argument) to null, and a third method that moves through the array and calls the methods in U. In main(), create a group of A objects and a single B. Fill the B with U references produced by the A objects. Use the B to call back into all the A objects. Remove some of the U references from the B.

I also added a couple lines of code to show that A's inner class has access to it's private methods.

package chapter.innerClasses;

interface U {
    void one();
    void two();
    void three();
}

class A {
    U getU() {
        return new U() {
            public void one() {System.out.println("one");}
            public void two() {System.out.println("two");}
            public void three() {System.out.println("three"); printSomething();}
        };
    }
    
    private void printSomething() {System.out.println("Something");}
}

class B {
    private U[] arrayOfU = new U[10];
    private int position = 0;

    public void storeU(U U_Reference) {
        if (position < 10 && position >= 0)
            arrayOfU[position++] = U_Reference;
    }
    
    public void setNull(int index) {
        if (index < 10 && index >= 0)
            arrayOfU[index] = null;
    }
    
    public void callU() {
        for (U myU : arrayOfU) {
            if (myU != null) {
                myU.one();
                myU.two();
                myU.three();
            }
        }
    }    
}

public class Excercise23 {
    public static void main(String[] args) {
        A firstA = new A(), secondA = new A();
        B theB = new B();
        theB.storeU(firstA.getU());
        theB.storeU(secondA.getU());
        theB.storeU(secondA.getU());
        theB.callU();
        theB.setNull(1);
        theB.callU();
    }
}