A.java

package com.freemindcafe.oops.innerclass.mypackage;

import com.freemindcafe.oops.innerclass.library.IMessageProvider;
import com.freemindcafe.oops.innerclass.library.MessageProcessor;


public class A {
    
    public static void main(String[] args) {
        MessageProcessor messageProcessor = new MessageProcessor();
        
        //Every classes objects can be passed
        //and can be used in other packages outside of this package.
        //These access qualifiers are applicable only at compile time.
        
        messageProcessor.process(new B());
        messageProcessor.process(new A().new C());
        messageProcessor.process(new D());
    }
    
    //nested static private class
    private static class B implements IMessageProvider{

        @Override
        public String provideMessage() {
            return "in B";
        }
        
    }
    
    //inner class (nested public class)
    public class C implements IMessageProvider{

        @Override
        public String provideMessage() {
            return "in C";
        }
        
    }
    
    //nested static public class
    public static class D implements IMessageProvider{

        @Override
        public String provideMessage() {
            return "in D";
        }
        
    }   

}