Generic.java

import java.util.ArrayList;

/**
 * A demonstration of the lack of multiple dispatch in Java
 * Notice how there is late dispatch on the object which owns "multi"
 *
 * (i.e the 'c' in `c.multi(o)`)
 * But there is only static dispatch on method arguments
 * (i.e the 'o' in `c.multi(o)`)
 *
 * The output will change based on whether it's A.multi or B.multi
 * but will always call the multi method defined for type X
 */

public class Generic{
	public static void main(String args[]){
		Generic g = new Generic();
	}
	public Generic(){
		A a = new Generic.A();
		B b = new B();

		ArrayList<X> os = new ArrayList<X>();// {new Object(), new X(), new Y(), new Z()};
		os.add(new X());
		os.add(new Y());
		os.add(new Z());

		ArrayList<Multi> cs = new ArrayList<Multi>();// {new Object(), new X(), new Y(), new Z()};
		cs.add(new A());
		cs.add(new B());

		for(Multi c: cs){
			for(X o: os){
				c.multi(o);
			}
		}
	}
	public interface Multi{
		public void multi(Object o);
		public void multi(String o);
		public void multi(X o);
		public void multi(Y o);
		public void multi(Z o);
	}

	public class A implements Multi{
		public void multi(Object o){
			System.out.println("The first type was A");
			System.out.println("The second type was Object");
		}
		public void multi(String o){
			System.out.println("The first type was A");
			System.out.println("The second type was String");
		}
		public void multi(X o){
			System.out.println("The first type was A");
			System.out.println("The second type was X");
		}
		public void multi(Y o){
			System.out.println("The first type was A");
			System.out.println("The second type was Y");
		}
		public void multi(Z o){
			System.out.println("The first type was A");
			System.out.println("The second type was Z");
		}
	}
	public class B implements Multi{
		public void multi(Object o){
			System.out.println("The first type was B");
			System.out.println("The second type was Object");
		}
		public void multi(String o){
			System.out.println("The first type was B");
			System.out.println("The second type was String");
		}
		public void multi(X o){
			System.out.println("The first type was B");
			System.out.println("The second type was X");
		}
		public void multi(Y o){
			System.out.println("The first type was B");
			System.out.println("The second type was Y");
		}
		public void multi(Z o){
			System.out.println("The first type was B");
			System.out.println("The second type was Z");
		}
	}
	public class X{

	}
	public class Y extends X{

	}
	public class Z extends Y{

	}
}