Inheritance and upcasting. : Inheritance « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Inheritance

class A {
  public void play() {
  }

  static void tune(A i) {
    i.play();
  }
}

// Wind objects are instruments
// because they have the same interface:
class B extends A {
}

public class MainClass {
  public static void main(String[] args) {
    B flute = new B();
    A.tune(flute); // Upcasting
  }

}