OnJava8-Examples/interfaces/music4/Music4.java

// interfaces/music4/Music4.java
// <20>2015 MindView LLC: see Copyright.txt
// Abstract classes and methods.
package interfaces.music4;
import polymorphism.music.Note;
import static com.mindviewinc.util.Print.*;

abstract class Instrument {
  private int i; // Storage allocated for each
  public abstract void play(Note n);
  public String what() { return "Instrument"; }
  public abstract void adjust();
}

class Wind extends Instrument {
  @Override
  public void play(Note n) {
    print("Wind.play() " + n);
  }
  @Override
  public String what() { return "Wind"; }
  @Override
  public void adjust() {}
}

class Percussion extends Instrument {
  @Override
  public void play(Note n) {
    print("Percussion.play() " + n);
  }
  @Override
  public String what() { return "Percussion"; }
  @Override
  public void adjust() {}
}

class Stringed extends Instrument {
  @Override
  public void play(Note n) {
    print("Stringed.play() " + n);
  }
  @Override
  public String what() { return "Stringed"; }
  @Override
  public void adjust() {}
}

class Brass extends Wind {
  @Override
  public void play(Note n) {
    print("Brass.play() " + n);
  }
  @Override
  public void adjust() { print("Brass.adjust()"); }
}

class Woodwind extends Wind {
  @Override
  public void play(Note n) {
    print("Woodwind.play() " + n);
  }
  @Override
  public String what() { return "Woodwind"; }
}

public class Music4 {
  // Doesn't care about type, so new types
  // added to the system still work right:
  static void tune(Instrument i) {
    // ...
    i.play(Note.MIDDLE_C);
  }
  static void tuneAll(Instrument[] e) {
    for(Instrument i : e)
      tune(i);
  }
  public static void main(String[] args) {
    // Upcasting during addition to the array:
    Instrument[] orchestra = {
      new Wind(),
      new Percussion(),
      new Stringed(),
      new Brass(),
      new Woodwind()
    };
    tuneAll(orchestra);
  }
}
/* Output:
Wind.play() MIDDLE_C
Percussion.play() MIDDLE_C
Stringed.play() MIDDLE_C
Brass.play() MIDDLE_C
Woodwind.play() MIDDLE_C
*/