music4.java

j2me软件教学

//: c07:music4:Music4.java
// Abstract classes and methods.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
package c07.music4;
import com.bruceeckel.simpletest.*;
import java.util.*;
import c07.music.Note;

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 {
  public void play(Note n) {
    System.out.println("Wind.play() " + n);
  }
  public String what() { return "Wind"; }
  public void adjust() {}
}

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

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

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

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

public class Music4 {
  private static Test monitor = new Test();
  // 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(int i = 0; i < e.length; i++)
      tune(e[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);
    monitor.expect(new String[] {
      "Wind.play() Middle C",
      "Percussion.play() Middle C",
      "Stringed.play() Middle C",
      "Brass.play() Middle C",
      "Woodwind.play() Middle C"
    });
  }
} ///:~