music5.java

《《Thinking in Java》中文版》包括：《Thinking in Java》和《ThinkInJava2000》

//: c08:music5:Music5.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// Interfaces.
import java.util.*;

interface Instrument {
  // Compile-time constant:
  int i = 5; // static & final
  // Cannot have method definitions:
  void play(); // Automatically public
  String what();
  void adjust();
}

class Wind implements Instrument {
  public void play() {
    System.out.println("Wind.play()");
  }
  public String what() { return "Wind"; }
  public void adjust() {}
}

class Percussion implements Instrument {
  public void play() {
    System.out.println("Percussion.play()");
  }
  public String what() { return "Percussion"; }
  public void adjust() {}
}

class Stringed implements Instrument {
  public void play() {
    System.out.println("Stringed.play()");
  }
  public String what() { return "Stringed"; }
  public void adjust() {}
}

class Brass extends Wind {
  public void play() {
    System.out.println("Brass.play()");
  }
  public void adjust() { 
    System.out.println("Brass.adjust()");
  }
}

class Woodwind extends Wind {
  public void play() {
    System.out.println("Woodwind.play()");
  }
  public String what() { return "Woodwind"; }
}

public class Music5 {
  // Doesn't care about type, so new types
  // added to the system still work right:
  static void tune(Instrument i) {
    // ...
    i.play();
  }
  static void tuneAll(Instrument[] e) {
    for(int i = 0; i < e.length; i++)
      tune(e[i]);
  }
  public static void main(String[] args) {
    Instrument[] orchestra = new Instrument[5];
    int i = 0;
    // Upcasting during addition to the array:
    orchestra[i++] = new Wind();
    orchestra[i++] = new Percussion();
    orchestra[i++] = new Stringed();
    orchestra[i++] = new Brass();
    orchestra[i++] = new Woodwind();
    tuneAll(orchestra);
  }
} ///:~