class Dog{ void bark(){ System.out.println("わん"); } } class Bird{ void twitter(){ System.out.println("ちゅん"); } } class Util{ static void sound(Dog d){ d.bark(); } static void sound(Bird b){ b.twitter(); } } class Main{ public static void main(String[] a){ Util.sound(new Dog()); Util.sound(new Bird()); } }