10. 将Rodent修改成一个接口。

package c10;

public class Pet {} ///:~

//: c10:Dog.java

package c10;

public class Dog extends Pet {} ///:~

//: c10:Pug.java

package c10;

public class Pug extends Dog {} ///:~

//: c10:Cat.java

package c10;

public class Cat extends Pet {} ///:~

//: c10:Rodent.java

package c10;

public class Rodent extends Pet {} ///:~

//: c10:Gerbil.java

package c10;

public class Gerbil extends Rodent {} ///:~

//: c10:Hamster.java

package c10;

public class Hamster extends Rodent {} ///:~

11. 在Adventure.java中，按照其它接口的样式，增加一个CanClimb接口。

interface CanFight {

void fight();

}

interface CanSwim {

void swim();

}

interface CanFly {

void fly();

}

class ActionCharacter {

public void fight() {}

}

class Hero extends ActionCharacter

implements CanFight, CanSwim, CanFly {

public void swim() {}

public void fly() {}

}

public class Adventure {

public static void t(CanFight x) { x.fight(); }

public static void u(CanSwim x) { x.swim(); }

public static void v(CanFly x) { x.fly(); }

public static void w(ActionCharacter x) { x.fight(); }

public static void main(String[] args) {

Hero h = new Hero();

t(h); // Treat it as a CanFight

u(h); // Treat it as a CanSwim

v(h); // Treat it as a CanFly

w(h); // Treat it as an ActionCharacter

}

} ///:~

2. 写一个程序，在其中导入并使用Month.java。

public final class Month {

private String name;

private Month(String nm) { name = nm; }

public String toString() { return name; }

public static final Month

JAN = new Month("January"),

FEB = new Month("February"),

MAR = new Month("March"),

APR = new Month("April"),

MAY = new Month("May"),

JUN = new Month("June"),

JUL = new Month("July"),

AUG = new Month("August"),

SEP = new Month("September"),

OCT = new Month("October"),

NOV = new Month("November"),

DEC = new Month("December");

public static final Month[] month = {

JAN, FEB, MAR, APR, MAY, JUN,

JUL, AUG, SEP, OCT, NOV, DEC

};

public static final Month number(int ord) {

return month[ord - 1];

}

public static void main(String[] args) {

Month m = Month.JAN;

System.out.println(m);

m = Month.number(12);

System.out.println(m);

System.out.println(m == Month.DEC);

System.out.println(m.equals(Month.DEC));

System.out.println(Month.month[3]);

}

3. 模仿Month.java中的例子，创建一周中每一天的一个枚举。

10. 将Rodent修改成一个接口。

package c10;

public class Pet {} ///:~

//: c10:Dog.java

package c10;

public class Dog extends Pet {} ///:~

//: c10:Pug.java

package c10;

public class Pug extends Dog {} ///:~

//: c10:Cat.java

package c10;

public class Cat extends Pet {} ///:~

//: c10:Rodent.java

package c10;

public class Rodent extends Pet {} ///:~

//: c10:Gerbil.java

package c10;

public class Gerbil extends Rodent {} ///:~

//: c10:Hamster.java

package c10;

public class Hamster extends Rodent {} ///:~

11. 在Adventure.java中，按照其它接口的样式，增加一个CanClimb接口。

interface CanFight {

void fight();

}

interface CanSwim {

void swim();

}

interface CanFly {

void fly();

}

class ActionCharacter {

public void fight() {}

}

class Hero extends ActionCharacter

implements CanFight, CanSwim, CanFly {

public void swim() {}

public void fly() {}

}

public class Adventure {

public static void t(CanFight x) { x.fight(); }

public static void u(CanSwim x) { x.swim(); }

public static void v(CanFly x) { x.fly(); }

public static void w(ActionCharacter x) { x.fight(); }

public static void main(String[] args) {

Hero h = new Hero();

t(h); // Treat it as a CanFight

u(h); // Treat it as a CanSwim

v(h); // Treat it as a CanFly

w(h); // Treat it as an ActionCharacter

}

} ///:~

2. 写一个程序，在其中导入并使用Month.java。

public final class Month {

private String name;

private Month(String nm) { name = nm; }

public String toString() { return name; }

public static final Month

JAN = new Month("January"),

FEB = new Month("February"),

MAR = new Month("March"),

APR = new Month("April"),

MAY = new Month("May"),

JUN = new Month("June"),

JUL = new Month("July"),

AUG = new Month("August"),

SEP = new Month("September"),

OCT = new Month("October"),

NOV = new Month("November"),

DEC = new Month("December");

public static final Month[] month = {

JAN, FEB, MAR, APR, MAY, JUN,

JUL, AUG, SEP, OCT, NOV, DEC

};

public static final Month number(int ord) {

return month[ord - 1];

}

public static void main(String[] args) {

Month m = Month.JAN;

System.out.println(m);

m = Month.number(12);

System.out.println(m);

System.out.println(m == Month.DEC);

System.out.println(m.equals(Month.DEC));

System.out.println(Month.month[3]);

}

3. 模仿Month.java中的例子，创建一周中每一天的一个枚举。