DuckTyping.java

package com.example;

import static java.lang.Thread.currentThread;
import static java.lang.reflect.Proxy.newProxyInstance;

interface Duck {
	void walk();

	void quack();

	/**
	 * Not implemented by {@link Elephant}.
	 */
	void doDucklikeThings();
}

interface Elephant {
	void walk();

	void quack();
}

final class ElephantImpl implements Elephant {
	@Override
	public void walk() {
		System.out.println("I'm an elephant, and I can walk");
	}

	@Override
	public void quack() {
		System.out.println("I'm a quacking elephant");
	}
}

class Main {
	public static void main(final String[] args) {
		final Elephant elephant = new ElephantImpl();

		final Duck duck = (Duck) newProxyInstance(currentThread().getContextClassLoader(),
				new Class[] {Elephant.class, Duck.class /* order matters */},
				(proxy, method, methodArgs) -> method.invoke(elephant, methodArgs));

		duck.walk();
		duck.quack();
		if (false) {
			duck.doDucklikeThings(); // will throw an IAE
		}
	}
}