类的高级特性（抽象类、接口等）

1、3、类的高级特性（抽象类、接口等）引入：本章继续深入学习面向对象思想。正课：1、抽象类 并不是所有的类都是用来描绘对象的，如果一个类中没有包含足够的信息来描绘一个具体的对象，这样的类就是抽象类。用abstract修饰。l 定义抽象类：abstract class 类名称 成员变量; 方法（）; /定义一般方法 abstract 方法（）; /定义抽象方法 范例testabstract：package testabstract;public abstract class Animal public Animal(String aType) type = new String(aType); pu

2、blic String toString() return "This is a " + type; / Dummy method to be implemented in the derived classes public abstract void sound(); private String type;package testabstract;public class Cat extends Animal public Cat(String aName) super("Cat"); / Call the base constructor nam

3、e = aName; / Supplied name breed = "Unknown" / Default breed value public Cat(String aName, String aBreed) super("Cat"); / Call the base constructor name = aName; / Supplied name breed = aBreed; / Supplied breed / Return a String full of a cat's details public String toString

4、() return super.toString() + "nIt's " + name + " the " + breed; / A miaowing method public void sound() System.out.println("Miiaooww"); private String name; / Name of a cat private String breed; / Cat breedpackage testabstract;public class Dog extends Animal public

5、Dog(String aName) super("Dog"); / Call the base constructor name = aName; / Supplied name breed = "Unknown" / Default breed value public Dog(String aName, String aBreed) super("Dog"); / Call the base constructor name = aName; / Supplied name breed = aBreed; / Supplied b

6、reed / Present a dog's details as a string public String toString() return super.toString() + "nIt's " + name + " the " + breed; / A barking method public void sound() System.out.println("Woof Woof"); private String name; / Name of a Dog private String breed; /

7、Dog breedpackage testabstract;public class Duck extends Animal public Duck(String aName) super("Duck"); / Call the base constructor name = aName; / Supplied name breed = "Unknown" / Default breed value public Duck(String aName, String aBreed) super("Duck"); / Call the b

8、ase constructor name = aName; / Supplied name breed = aBreed; / Supplied breed / Return a String full of a duck's details public String toString() return super.toString() + "nIt's " + name + " the " + breed; / A quacking method public void sound() System.out.println("

9、;Quack quackquack"); private String name; / Duck name private String breed; / Duck breedpackage testabstract;class Spaniel extends Dog public Spaniel(String aName) super(aName, "Spaniel"); package testabstract;import java.util.Random;public class TestAbstract public static void main(S

10、tring args) / Create an array of three different animals Animal theAnimals = new Dog("Rover", "Poodle"), new Cat("Max", "Abyssinian"), new Duck("Daffy","Aylesbury"), new Spaniel("Fido") ; Animal petChoice; / Choice of pet Random s

11、elect = new Random(); / Random number generator / Make five random choices of pet for(int i = 0; i < 5; i+) / Choose a random animal as a pet petChoice = theAnimalsselect.nextInt(theAnimals.length); System.out.println("nYour choice:n" + petChoice); petChoice.sound(); / Get the pet's

12、 reaction 2、接口接口可以被用来实现类间多继承结构。接口内部只能定义 public 的抽象方法和静态的、公有常量，因此所有的方法需要在子类中实现。接口定义方法：l 访问权限 interface 接口名称 extends 父接口名1，父接口名2,. /接口体程序 范例testinterface：package testinterface;public class Cat implements PetOutput public Cat(String aName) /super("Cat"); / Call the base constructor name = aNa

13、me; / Supplied name breed = "Unknown" / Default breed value public Cat(String aName, String aBreed) /super("Cat"); / Call the base constructor name = aName; / Supplied name breed = aBreed; / Supplied breed / Return a String full of a cat's details public String toString() ret

14、urn "nIt's " + name + " the " + breed; / A miaowing method public void sound() System.out.println("Miiaooww"); private String name; / Name of a cat private String breed; / Cat breedpackage testinterface;public class Dog implements PetOutput public Dog(String aName)

15、name = aName; / Supplied name breed = "Unknown" / Default breed value public Dog(String aName, String aBreed) name = aName; / Supplied name breed = aBreed; / Supplied breed / Present a dog's details as a string public String toString() return "It's " + name + " the &

16、quot; + breed; / A barking method public void sound() System.out.println("Woof Woof"); public String getName() return name; private String name; / Name of a dog private String breed; / Dog breedpackage testinterface;public class Duck implements PetOutput public Duck(String aName) /super(&q

17、uot;Duck"); / Call the base constructor name = aName; / Supplied name breed = "Unknown" / Default breed value public void layEgg() System.out.println("Egg laid"); public Duck(String aName, String aBreed) /super("Duck"); / Call the base constructor name = aName; / S

18、upplied name breed = aBreed; / Supplied breed / Return a String full of a duck's details public String toString() return "nIt's " + name + " the " + breed; / A quacking method public void sound() System.out.println("Quack quackquack"); private String name; / Duc

19、k name private String breed; / Duck breedpackage testinterface;public interface PetOutput void sound();package testinterface;public interface Read1 void readNewspaper();package testinterface;/import testabstract.Read;class Spaniel extends Dog implements Read1 public Spaniel(String aName) super(aName

20、, "Spaniel"); public void readNewspaper( ) System.out.println("I can read Newspaper"); package testinterface;import java.util.Random;public class TestInterface public static void main(String args) / PetOutput thePets = / Dog("Rover", "Poodle"), / new Cat("Max", "Abyssini