public enum Note {
 // 演奏樂(lè)符
    MIDDLE_C, C_SHARP, B_FLAT;

}
public class Instrument {

 // 樂(lè)器基類
    public void play(Note n) {
        print("Instrument.play()");
    }

}
public class Wind extends Instrument{

 // Wind是一個(gè)具體的樂(lè)器
    // Redefine interface method:
    public void play(Note n) {
        System.out.println("Wind.play() " + n);
    }

}
public class Music {

 // 樂(lè)器進(jìn)行演奏
    public static void tune(Instrument i) {
        i.play(Note.MIDDLE_C);
    }

    public static void main(String[] args) {
        Wind flute = new Wind();
        tune(flute); // 向上轉(zhuǎn)型
    }
}

class Stringed extends Instrument {
    public void play(Note n) {
        print("Stringed.play() " + n);
    }
}


class Brass extends Instrument {
    public void play(Note n) {
        print("Brass.play() " + n);
    }
}


public class Music2 {
    public static void tune(Wind i) {
        i.play(Note.MIDDLE_C);
    }

    public static void tune(Stringed i) {
        i.play(Note.MIDDLE_C);
    }


    public static void tune(Brass i) {
        i.play(Note.MIDDLE_C);

    }
    public static void main(String[] args) {
        Wind flute = new Wind();
        Stringed violin = new Stringed();
        Brass frenchHorn = new Brass();
        tune(flute); // No upcasting
        tune(violin);
        tune(frenchHorn);
    }
}

public static void tune(Instrument i) {
    // ...
    i.play(Note.MIDDLE_C);

}

class Instrument {
    void play(Note n) { print("Instrument.play() " + n); }
    String what() { return "Instrument"; }
    void adjust() { print("Adjusting Instrument"); }
}


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


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

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


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


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


public class Music3 {
    // Doesn't care about type, so new types
    // added to the system still work right:
    public static void tune(Instrument i) {
        // ...
        i.play(Note.MIDDLE_C);
    }

    public 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);
    }
}

public class Glyph {

    void draw() { print("Glyph.draw()"); }
    Glyph() {
        print("Glyph() before draw()");
        draw(); // 調(diào)用正在構(gòu)造的對(duì)象的某個(gè)動(dòng)態(tài)綁定方法，對(duì)象的字段radius被初始化為0
        print("Glyph() after draw()");
    }

}


public class RoundGlyph extends Glyph{

    private int radius = 1;

    RoundGlyph(int r) {
        radius = r;
        print("RoundGlyph.RoundGlyph(), radius = " + radius);
    }
    void draw() {
        print("RoundGlyph.draw(), radius = " + radius);
    }


}


public class PolyConstructors {
    
    public static void main(String[] args) {
        new RoundGlyph(5);
    }
    
}

/* Output:
    Glyph() before draw()
    RoundGlyph.draw(), radius = 0
    Glyph() after draw()
    RoundGlyph.RoundGlyph(), radius = 5
*///:~

import java.io.ByteArrayInputStream;
import java.io.InputStream;

class Base
{
    //子類Derive將重寫此方法，將返回類型設(shè)置為InputStream的子類
   public InputStream getInput()
   {
    　　return System.in;
   }
}
public  class Derive extends Base
{

    @Override
    public ByteArrayInputStream getInput()
    {

        return new ByteArrayInputStream(new byte[1024]);
    }
    public static void main(String[] args)
    {
        Derive d=new Derive();
        System.out.println(d.getInput().getClass());
    }
}
/*程序輸出：
class java.io.ByteArrayInputStream
*/

class Actor {
 public void act() {
 }
}
 
class HappyActor extends Actor {
 public void act() {
  System.out.println("HappyActor");
 }
}
 
class SadActor extends Actor {
 public void act() {
  System.out.println("SadActor");
 }
}
 
class Stage {
 private Actor actor = new HappyActor();
 
 public void change() {
  actor = new SadActor();
 }
 
 public void performPlay() {
  actor.act();
 }
}
 
public class Transmogrify {
 public static void main(String[] args) {
  Stage stage = new Stage();
  stage.performPlay();
  stage.change();
  stage.performPlay();
 }
 
}