Upcasting

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//: Music.java 
// Inheritance & upcasting
package c07;
 
class Note {
  private int value;
  private Note(int val) { value = val; }
  public static final Note
    middleC = new Note(0),
    cSharp = new Note(1),
    cFlat = new Note(2);
} // Etc.
 
class Instrument {
  public void play(Note n) {
    System.out.println("Instrument.play()");
  }
}
 
// Wind objects are instruments
// because they have the same interface:
class Wind extends Instrument {
  // Redefine interface method:
  public void play(Note n) {
    System.out.println("Wind.play()");
  }
}
 
public class Music {
  public static void tune(Instrument i) {
    // ...
    i.play(Note.middleC);
  }
  public static void main(String[] args) {
    Wind flute = new Wind();
    tune(flute); // Upcasting
  }
} ///:~ 

//: Music2.java 
// Overloading instead of upcasting
 
class Note2 {
  private int value;
  private Note2(int val) { value = val; }
  public static final Note2
    middleC = new Note2(0),
    cSharp = new Note2(1),
    cFlat = new Note2(2);
} // Etc.
 
class Instrument2 {
  public void play(Note2 n) {
    System.out.println("Instrument2.play()");
  }
}
 
class Wind2 extends Instrument2 {
  public void play(Note2 n) {
    System.out.println("Wind2.play()");
  }
}
 
class Stringed2 extends Instrument2 {
  public void play(Note2 n) {
    System.out.println("Stringed2.play()");
  }
}
 
class Brass2 extends Instrument2 {
  public void play(Note2 n) {
    System.out.println("Brass2.play()");
  }
}
 
public class Music2 {
  public static void tune(Wind2 i) {
    i.play(Note2.middleC);
  }
  public static void tune(Stringed2 i) {
    i.play(Note2.middleC);
  }
  public static void tune(Brass2 i) {
    i.play(Note2.middleC);
  }
  public static void main(String[] args) {
    Wind2 flute = new Wind2();
    Stringed2 violin = new Stringed2();
    Brass2 frenchHorn = new Brass2();
    tune(flute); // No upcasting
    tune(violin);
    tune(frenchHorn);
  }
} ///:~