interface Hello {
    void hello();
}
 
class World implements Hello {
    public void hello() { System.out.println("Hello, World!"); }
}
 
class Greeter implements Hello {
    private String name;
 
    Greeter(String name) { this.name = name; }
 
    public void hello() { System.out.println("Hello," + this.name + "!"); }
}
 
class Main {
    public static void main(String[] args) {
        Hello world = new World();
        Hello greeter = new Greeter("Programowanie Obiektowe");
 
        world.hello();
        greeter.hello();
    }
}

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