Java编程思想第四版第八章练习

练习1：创建一个Cycle类，它具有子类Unicycle，Bicycle和TriCycle.演示每一个类型的实例都可以经由ride（）向上转型为Cycle。

public class Exercise8_1 {    static void ride(Cycle c) {    }     public static void main(String[] args) {          ride(new Unicycle());          ride(new Bicycle());          ride(new Tricycle());    }}class Unicycle extends Cycle{}class Bicycle extends Cycle{}class Tricycle extends Cycle{}

练习2： 在几何图形的示例中添加@Override注解。

public class Shape {      public void draw() {}      public void erase() {}    }

public class Circle extends Shape {     @Override public void draw() { System.out.println("Circle.draw()"); }     @Override public void erase() {System.out.println("Circle.erase()"); }    }

public class Square extends Shape {    @Override public void draw() { System.out.println("Square.draw()"); }    @Override public void erase() { System.out.println("Square.erase()"); }    }

public class Triangle extends Shape {    @Override public void draw() {System.out.println("Triangle.draw()"); }    @Override public void erase() { System.out.println("Triangle.erase()"); }    }

public class Shapes {      private static RandomShapeGenerator gen =        new RandomShapeGenerator();      public static void main(String[] args) {        Shape[] s = new Shape[9];        // Fill up the array with shapes:        for(int i = 0; i < s.length; i++)          s[i] = gen.next();        // Make polymorphic method calls:        for(Shape shp : s)          shp.draw();      }    }

练习3：在基类Shape（）.java中添加一个新方法，用于打印一条消息，但导出类中不要覆盖这个方法。请解释发生了什么。现在，在其中一个导出类中覆盖该方法，而在其他的导出类不予覆盖，观察又有什么发生。最后，在所有的导出类中覆盖这个方法。

public class Circle extends Shape {     @Override public void draw() { System.out.println("Circle.draw()"); }     @Override public void erase() {System.out.println("Circle.erase()"); }              public void msg() {                  System.out.println("Circle.msg");              }    }

public class Square extends Shape {    @Override public void draw() { System.out.println("Square.draw()"); }    @Override public void erase() { System.out.println("Square.erase()"); }     public void msg() {      System.out.println("Square.msg");     }    }

public class Triangle extends Shape {    @Override public void draw() {System.out.println("Triangle.draw()"); }    @Override public void erase() { System.out.println("Triangle.erase()"); }          public void msg() {              System.out.println("Triangle.msg");     }    }

public class Shape {      public void draw() {}      public void erase() {}      public void msg() {          System.out.println("Shape.msg()");      }    }

public class Shapes {      private static RandomShapeGenerator gen =        new RandomShapeGenerator();      public static void main(String[] args) {        Shape[] s = new Shape[9];        // Fill up the array with shapes:        for(int i = 0; i < s.length; i++)          s[i] = gen.next();        // Make polymorphic method calls:        for(Shape shp : s) {            shp.draw();            shp.msg();        }      }    }

练习4：向Shape.java中添加一个新的Shape类型，并在main（）方法中验证：多态对新类型的作用是否与在旧类型中的一样。

public class Shapes {      public static void main(String[] args) {        Shape[] s = {new Square(), new Triangle(),new Terahedron(),new Circle()};        for(Shape shp : s) {            shp.draw();            shp.msg();        }      }    }

    public class Terahedron extends Shape{    public void draw() {        System.out.println("Terahedron.draw()");    }    public void erase() {        System.out.println("Terahedron.erase()");    }        public void msg() {            System.out.println("Terahedron.msg()");        }}

练习5：以练习1为基础，在Cycle中添加wheels（）方法，它将返回轮子的数量。修改ride（）方法，并验证多态起作用了。

public class Exercise8_5 {    static void ride(Cycle c) {        System.out.println("Number of wheels : "+c.wheels());    }     public static void main(String[] args) {          ride(new Unicycle());          ride(new Bicycle());          ride(new Tricycle());    }}class Cycle{    public int wheels() {        return 0;    }}class Unicycle extends Cycle{    public int wheels() {        return 1;    }}class Bicycle extends Cycle{    public int wheels() {        return 2;    }}class Tricycle extends Cycle{    public int whee`s() {        return 3;    }}

练习6：修改Music3.java，使what（）方法成为根Object的toString方法.试用System.out.Printfln()方法打印Instrucment对象（不用向上转型）

class Instrument {  void play(Note n) { System.out.println("Instrument.play() " + n); }    public String toString() {        return "Instrument";    }  void adjust() { System.out.println("Adjusting Instrument"); }}class Wind extends Instrument {  void play(Note n) { System.out.println("Wind.play() " + n); }    public String toString() {        return "Wind";    }  void adjust() { System.out.println("Adjusting Wind"); }}   class Percussion extends Instrument {  void play(Note n) { System.out.println("Percussion.play() " + n); }  public String toString() {        return "Percussion";    }  void adjust() { System.out.println("Adjusting Percussion"); }}class Stringed extends Instrument {  void play(Note n) { System.out.println("Stringed.play() " + n); }  public String toString() {      return "Stringed";    }  void adjust() { System.out.println("Adjusting Stringed"); }}class Brass extends Wind {  void play(Note n) { System.out.println("Brass.play() " + n); }  void adjust() { System.out.println("Adjusting Brass"); }}class Woodwind extends Wind {  void play(Note n) {System.out.println("Woodwind.play() " + n); }  public String toString() {      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);         System.out.println(i.toString());    }  }   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);  }}

练习7：想Music3.java添加一个新的类型Instrument，并验证多态性是否作用于所添加的新类型。

public class Exercise8_7 {    public static void main(String[] args) {          Instrument[] orchestra = {                  new Wind(),                  new Percussion(),                  new Stringed(),                  new Brass(),                  new Woodwind(),                  new Electronic()                };          for(Instrument i:orchestra) {              i.play(Note.MIDDLE_C);              System.out.println(i);              i.adjust();          }    }} class Electronic extends Instrument{     void play(Note n) { System.out.println("Electronic.play() " + n); }        public String toString() {            return "Electronic";        } }

练习8：修改Music3.java，使其可以像Shapes.java中的方式那样可以随机创建Instrument对象

public class Exercise8_8 {      public static void main(String[] args) {        InstrumentGenerator generator =new InstrumentGenerator();        for (int i = 0; i < 20; i++) {            System.out.println(generator.next());        }    }}class InstrumentGenerator{    Random random = new Random(47);    public Instrument next() {        switch (random.nextInt(6)) {        default:        case 0: return new Wind();        case 1: return new Percussion();        case 2: return new Stringed();        case 3: return new Brass();        case 4: return new Woodwind();        case 5: return new Electronic`);        }    }}

练习9：创建Rodent（啮齿动物）：Mnouse（老鼠），Gerbil（鼹鼠），Hamster（大颊鼠），等等这样一个的继承层次结构。在基类中，提供对所有的Rodent都通用的方法，在导出类中，根据特定的Rodent类型覆盖这些方法，以便它们执行不同的行为。创建一个Robent数组，填充不同的Rodent类型，然后调用基类方法，观察发生什么情况。**

public class Exercise8_9 {    public static void main(String[] args) {         Rodent rodents[] = {new Mouse(),new Gerbil(),new Hamster()};         for(Rodent r: rodents) {             r.hop();             r.scurry();             r.reproduce();             System.out.println(r);         }    }}class Rodent{    public void hop() {System.out.println("Rodent hopping");}    public void scurry() {System.out.println("Rodent scurrying");}    public void reproduce() {System.out.println("Making more Rodent");}    public String toString() {return "Eodent";}}class Mouse extends Rodent{    public void hop() {System.out.println("Mouse hopping");}    public void scurry() {System.out.println("Mouse scurrying");}    public void reproduce() {System.out.println("Making more Mice");}    public String toString() {return "Mouse";}}class Gerbil extends Rodent{    public void hop() {System.out.println("Gerbil hopping");}    public void scurry() {System.out.println("Gerbil scurrying");}    public void reproduce() {System.out.println("Making more Gerbil");}    public String toString() {return "Gernil";}}class Hamster extends Rodent{    public void hop() {System.out.println("Hamster hopping");}    public void scurry() {System.out.println("Hamster scurrying");}    public void reproduce() {System.out.println("Making more Hamster");}    public String toString() {return "Hamster";}}

练习10: 创建一个包含两个方法的基类。在第一个方法中可以调用第二个方法。然后产生一个继承自该基类的导出类，且覆盖基类中的第二个方法。为该导出类创建一个对象，将他向上转型到基类并调用第一个方法，解释发生的情况。

public class Exercise8_10 {   public static void main(String[] args) {      TwoMethods twoMethods = new Inherited();      twoMethods.m1();}}class TwoMethods{    public void m1() {        System.out.println("Inside m1,calling m2");        m2();    }    public void m2() {        System.out.println("Inside m2");    }}class Inherited extends TwoMethods{    public void m2() {        System.out.println("Inside Inherited.m2");    }}

练习11： 向Sandwich.java中添加 Pickle类。

class Pickle {      Pickle() { System.out.println("Pickle()"); }    }class Meal {      Meal() { System.out.println("Meal()"); }    }    class Bread {      Bread() { System.out.println("Bread()"); }    }    class Cheese {      Cheese() { System.out.println("Cheese()"); }    }    class Lettuce {      Lettuce() { System.out.println("Lettuce()"); }    }    class Lunch extends Meal {      Lunch() { System.out.println("Lunch()"); }    }    class PortableLunch extends Lunch {      PortableLunch() { System.out.println("PortableLunch()");}    }    public class Sandwich extends PortableLunch {              Bread b = new Bread();              Cheese c = new Cheese();              Lettuce l = new Lettuce();              Pickle p = new Pickle();      public Sandwich() { System.out.println("Sandwich()"); }      public static void main(String[] args) `        new Sandwich();      }    }

练习12：修改练习9，使其能够演示基类和导出类的初始化顺序。然后向基类和导出类中添加成员对象，并说明构造期间初始化发生的顺序。

public class Exercise8_12 {    public static void main(String[] args) {         new Hamster2();    }}class Member{    public Member(String id) {        System.out.println("Member contructor"+id);    }}class Rodent2{    Member m1 = new Member("r1"),m2 = new Member("r2");    public Rodent2() {System.out.println("Rodent Conteuctor");}    public void hop() {System.out.println("Rodent hopping");}    public void scurry() {System.out.println("Rodent scurrying");}    public void reproduce() {System.out.println("Making more Rodent");}    public String toString() {return "Eodent";}}class Mouse2 extends Rodent2{    Member m1 = new Member("m1"),m2 = new Member("m2");    public Mouse2() {System.out.println("Mouse Conteuctor");}    public void hop() {System.out.println("Mouse hopping");}    public void scurry() {System.out.println("Mouse scurrying");}    public void reproduce() {System.out.println("Making more Mice");}    public String toString() {return "Mouse";}}class Gerbil2 extends Rodent2{    Member m1 = new Member("G1"),m2 = new Member("G2");    public Gerbil2() {System.out.println("Gerbil Conteuctor");}    public void hop() {System.out.println("Gerbil hopping");}    public void scurry() {System.out.println("Gerbil scurrying");}    public void reproduce() {System.out.println("Making more Gerbil");}    public String toString() {return "Gernil";}}class Hamster2 extends Rodent2{    Member m1 = new Member("h1"),m2 = new Member("h2");    public Hamster2() {System.out.println("Hamster Conteuctor");}    public void hop() {System.out.println("Hamster hopping");}    public void scurry() {System.out.println("Hamster scurrying");}    public void reproduce() {System.out.println("Making more Hamster");}    public String toString() {return "Hamster";}}

练习13 ： 在ReferenceCounting.java中添加一个finalized（）方法，用来校验终止条件

class Shared {      private int refcount = 0;      private static long counter = 0;      private final long id = counter++;      public Shared() {          System.out.println("Creating " + this);      }      public void addRef() { refcount++; }      protected void dispose() {        if(--refcount == 0)              System.out.println("Disposing " + this);      }      public String toString() { return "Shared " + id; }    protected void finalize() {         if(refcount!=0) {              System.out.println("ERROR : object is not properly clean-up");         }    }    }    class Composing {      private Shared shared;      private static long counter = 0;      private final long id = counter++;      public Composing(Shared shared) {          System.out.println("Creating " + this);        this.shared = shared;        this.shared.addRef();      }      protected void dispose() {        System.out.println("disposing " + this);        shared.dispose();      }      public String toString() { return "Composing " + id; }    }    public class ReferenceCounting {      public static void main(String[] args) {        Shared shared = new Shared();        Composing[] composing = { new Composing(shared),          new Composing(shared), new Composing(shared),          new Composing(shared), new Composing(shared) };        for(Composing c : composing)          c.dispose();        new Composing(new Shared());        System.gc();      }    }

修改练习12，使其某个成员对象变为具有引用计数的共享对象，并证明它可以正常运行。

public class Exercise8_14 {    public static void main(String[] args) {        SharedMember member = new SharedMember();        Rodent3[] rodents = {                new Mouse3(member),                new Gerbil3(member),                new Hamster3(member)                };        for(Rodent3 r:rodents) {            r.dispose();        }    }}class NonSharedMember{    public NonSharedMember(String id) {        System.out.println("NonSharedMember contructor"+id);    }}class SharedMember{    private int Recount;    public void addRef() {        System.out.println("Number of reference:" + ++Recount);    }    public void dispose() {        if(--Recount==0) {            System.out.println("Disposing"+this);        }    }    public SharedMember(){      System.out.println("SharedMember Constructor");       }    public String toString() {        return "SharedMemebr";    }}class Rodent3{    private SharedMember sharedMember;    Member m1 = new Member("r1"),m2 = new Member("r2");    public Rodent3(SharedMember sharedMember) {        System.out.println("Rodent Conteuctor");        this.sharedMember = sharedMember;        this.sharedMember.addRef();        }    protected void dispose() {        System.out.println("Disposing "+this);        sharedMember.dispose();    }    public void hop() {System.out.println("Rodent hopping");}    public void scurry() {System.out.println("Rodent scurrying");}    public void reproduce() {System.out.println("Making more Rodent");}    public String toString() {return "Eodent";}}class Mouse3 extends Rodent3{    Member m1 = new Member("m1"),m2 = new Member("m2");    public Mouse3(SharedMember sharedMember) {        super(sharedMember);        System.out.println("Mouse Conteuctor");    }    public void hop() {System.out.println("Mouse hopping");}    public void scurry() {System.out.println("Mouse scurrying");}    public void reproduce() {System.out.println("Making more Mice");}    public String toString() {return "Mouse";}}class Gerbil3 extends Rodent3{    Member m1 = new Member("G1"),m2 = new Member("G2");    public Gerbil3(SharedMember sharedMember) {        super(sharedMember);        System.out.println("Gerbil Conteuctor");}    public void hop() {System.out.println("Gerbil hopping");}    public void scurry() {System.out.println("Gerbil scurrying");}    public void reproduce() {System.out.println("Making more Gerbil");}    public String toString() {return "Gernil";}}class Hamster3 extends Rodent3{    Member m1 = new Member("h1"),m2 = new Member("h2");    public Hamster3(SharedMember sharedMember) {        super(sharedMember);         System.out.println("Hamster Conteuctor");        }    public void hop() {System.out.println("Hamster hopping");}    public void scurry() {System.out.println("Hamster scurrying");}    public void reproduce() {System.out.println("Making more Hamster");}    public String toString() {return "Hamster";}}

练习15： 在PolyConstructors.java中添加一个RectangularGlyph，并证明会出现本节所描述的问题

//PolyConstructors.javaclass Glyph {      void draw() {  System.out.println("Glyph.draw()"); }      Glyph() {          System.out.println("Glyph() before draw()");       draw();        System.out.println("Glyph() after draw()");      }    }       class RoundGlyph extends Glyph {      private int radius = 1;      RoundGlyph(int r) {        radius = r;        System.out.println("RoundGlyph.RoundGlyph(), radius = " + radius);      }      void draw() {        System.out.println("RoundGlyph.draw(), radius = " + radius);      }    }       public class PolyConstructors {      public static void main(String[] args) {        new RoundGlyph(5);      }    }

public class Exercise8_15 {    public static void main(String[] args) {        new RoundGlyph(5);        new RectangularGlyph(2, 2);    }}class RectangularGlyph extends Glyph{    private int width = 4;    private int height = 5;    public RectangularGlyph(int width,int height) {        this.width = width;        this.height = height;        System.out.println("RectangularGlyph.width = "+width+" height = "+height);    }    public void draw() {        System.out.println("RectangularGlyph.area = "+(width*height));    }}

练习16： 遵循Transmogrify.java这个例子，创建一个Starship类，包含一个AlertStatus引用，此引用可以指示三种不同的状态。纳入一些可以改变这些状态的方法

public class Exercise8_16 {     public static void main(String[] args) {        Starship starship = new Starship();        System.out.println(starship);        starship.change(new YellowAlertStatus());        System.out.println(starship);        starship.change(new RedAlertStatus());        System.out.println(starship);    }}class AlertStatus{    public String getStatus() {        return "None";    }}class RedAlertStatus extends AlertStatus{    public String getStatus() {        return "Red";    }}class YellowAlertStatus extends AlertStatus{    public String getStatus() {        return "Yellow";    }}class GreenAlertStatus extends AlertStatus{    public String getStatus() {        return "Green";    }}class Starship{    private AlertStatus alertStatus = new GreenAlertStatus();    public void change(AlertStatus iStatus) {        alertStatus = iStatus;    }    public String toString() {        return alertStatus.getStatus();    }}

练习17：使用练习1中的Cycle的层次结构哦，在Unicycle 和Bicycle中添加balance方法，而Tricycle中国不添加。创建这三种类型的实例，并将他们向上转型为Cycle数组。在该数组的每一个元素上都尝试调用balance，并观察结果。然后将他们向下转型，再次调用balance（），并观察将所发生什么。

public class Exercise8_17 {   public static void main(String[] args) {       Cycle3 []cycle = {new Unicycle3(),new Bicycle3(),new Tricycle3()};//     cycle[0].balance();//     cycle[1].balance();//     cycle[2].balance();       ((Unicycle3) cycle[0]).balance();       ((Bicycle3) cycle[1]).balance();     //  ((Tricycle3) cycle[2]).balance();}}class Cycle3{}class Unicycle3 extends Cycle3{    public void balance() {};}class Bicycle3 extends Cycle3{    public void balance() {};}class Tricycle3 extends Cycle3{}