To run, download and run "javac *.java && java Main".

Animal.java

class Animal {
	void bark(Animal a) {
		System.out.println("bark(Animal a) in Animal");
	};
	void bark(Dog d) {
		System.out.println("bark(Dog a) in Animal");
	};
}

Dog.java

class Dog extends Animal {
	/* Try commenting this method out and see what happens! */
	void bark(Animal a) {
		System.out.println("bark(Animal a) in Dog");
	};
	void bark(Dog d) {
		System.out.println("bark(Dog d) in Dog");
	};
}

Main.java

class Main {
	public static void main(String[] args) {
		Animal a = new Dog();
		a.bark(a);
	}
}