1. Interface & Inner classes
Chapter 7
Interface & Inner classes

2. super class Pet :

3. public class Pet {
public void speak() {
System.out.println("I am a generic pet."); }
public class Dog extends Pet {
public void speak() {
System.out.println("Woof");
public class Cat extends Pet {
System.out.println("Meow");
public class Bird extends Pet {
System.out.println("Tweedle ");

4. public class TestAnimals {
public static void main(String args[]) {
Pet myPets[] = new Pet[4];
myPets[0] = new Pet();
myPets[1] = new Cat();
myPets[2] = new Bird();
myPets[3] = new Dog();
for (int index=0; index<4; index++) 
myPets[index].speak(); }
Result：
Java
I am a generic pet.
Meow
Tweedle
Woof
Output completed (0 sec consumed) - Normal Termination

6. abstract class Pet {
public abstract void speak(); }
public class Dog extends Pet {
public void speak() {
System.out.println("Woof");
public class Cat extends Pet {
System.out.println("Meow");
public class Bird extends Pet {
System.out.println("Tweedle");

7. public class TestAnimals {
public static void main(String args[ ]) {
Pet myPets[] = new Pet[4];
myPets[0] = new Bird();
myPets[1] = new Cat();
myPets[2] = new Bird();
myPets[3] = new Dog();
for (int index=0; index<4; index++)
myPets[index].speak(); }
Result：
Java
Tweedle
Meow
Woof
Output completed (0 sec consumed) - Normal Termination

8. interface Pet :

9. public abstract void speak(); } public class Dog implements Pet {
interface Pet {
public abstract void speak(); }
public class Dog implements Pet {
public void speak() {
System.out.println("Woof");
public class Cat implements Pet {
System.out.println("Meow");
public class Bird implements Pet {
System.out.println("Tweedle");
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10. public class TestAnimals {
public static void main(String args[]) {
Pet myPets[] = new Pet[4];
myPets[0] = new Bird();
myPets[1] = new Cat();
myPets[2] = new Bird();
myPets[3] = new Dog();
for (int index=0; index<4; index++)
myPets[index].speak(); }
Result：
Java
Tweedle
Meow
Woof
Output completed (0 sec consumed) - Normal Termination

11. contract：契约、合同

12. revealing：展现或显示(某物)的, 显露的

13. Simulating multiple inheritance

15. public abstract class Animal {
protected int legs;
protected Animal(int legs) {
this.legs = legs; }
public abstract void eat();
public void walk() {
System.out.println("This animal walks on " + legs + " legs.");

16. public interface Pet {
public abstract void setName(String name);
public abstract String getName();
public abstract void speak();
public abstract void play(); }
public class Bird extends Animal implements Pet {
private String name;
public Bird() {
super(2); // 这行是必需的 }
public void setName(String name) {
this.name = name;
public String getName() {
return name;

17. public void speak() {
System.out.println("speak:Tweedle"); }
public void play() {
System.out.println("play:Birds fly on the sky all day.");
//Bird 覆盖父类Animal 的方法walk()
public void walk() {
//super.walk();
System.out.println("walk:Birds, of course, can't walk; they fly .");
//Bird 覆盖父类Animal 的抽象方法eat()
public void eat() {
System.out.println("eat:Birds eat corn .");
//Bird 创建自己的方法buildNest()
public void buildNest() {
System.out.println("buildNest: Birds buid the nest within the branches.");
//Bird 创建自己的方法layEggs()
public void layEggs() {
System.out.println("layEggs: Birds lay eggs.");

18. public class Cat extends Animal implements Pet {
private String name;
public Cat(String name) {
super(4);
this.name = name; }
public Cat() {
this("");
public void setName(String name) {
public String getName() {
return name;
public void speak() {
System.out.println("speak:Meow");
cpublic void play() {
System.out.println("play:"+name + " likes to play with string.");
//Cat 覆盖父类Animal 的抽象方法eat()
public void eat() {
System.out.println("eat:Cats like to eat spiders and mice.");

19. public class Spider extends Animal {
public Spider() {
super(8); }
//Spider 覆盖父类Animal 的抽象方法eat()
public void eat() {
System.out.println("eat:Spiders catch flies in their webs to eat.");

20. public class TestAnimals { public static void main(String[] args) {
Bird b = new Bird();
Cat c = new Cat("Fluffy");
Animal ab = new Bird();
Animal as = new Spider();
Pet p = new Cat(); //允许定义接口类型的变量
//示例对接口的不同实现
b.speak(); //调用Bird类对接口Pet的实现
b.play(); //调用Bird类对接口Pet的实现
b.eat();
b.walk();
p.speak(); //通过接口类型的变量p访问Cat实现的接口方法
c.play(); //调用Cat类对接口Pet的实现
c.eat();
c.walk();
as.eat();
as.walk();
((Bird)ab).speak();
ab.walk(); }
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21. Result：
Java
speak:Tweedle
play:Birds fly on the sky all day.
eat:Birds eat corn .
walk:Birds, of course, can't walk; they fly .
speak:Meow
play:Fluffy likes to play with string.
eat:Cats like to eat spiders and mice.
This animal walks on 4 legs.
eat:Spiders catch flies in their webs to eat.
This animal walks on 8 legs.
Output completed (0 sec consumed) - Normal Termination

22. Many unrelated classes can implement the same interface
A class can implement many unrelated interfaces

23. Multiple Interface Example

24. Multiple Interface Example

25. Multiple Interface Example

26. Multiple Interface Example

30. // OuterNested1.java
public class OuterNested1
private int size;
/* 声明名为Nested的嵌套类 */
public class Nested {
public int doStuff() {
// 嵌套类可以访问OuterNested1类的私有成员size变量
return(size++); }
public int testTheNested() {
Nested i = new Nested();
return(i.doStuff());
// TestOuterNested1.java
public class TestOuterNested1 {
public static void main(String[] args) {
OuterNested1 outer = new OuterNested1();
System.out.println(outer.testTheNested());
Result： 0

32. // OuterNested2.java
public class OuterNested2 {
private int size;
public class Nested {
public int doStuff() {
return(++size); }
// TestOuterNested2.java
public class TestOuterNested2 {
public static void main(String[] args) {
OuterNested2 outer = new OuterNested2();
//创建OuterNested2类的嵌套对象必须通过OuterNested2的对象引用
OuterNested2.Nested nested = outer.new Nested();
System.out.println(nested.doStuff());
Reault： 1

34. // OuterNested3.java
public class OuterNested3 {
private int size;
public class Nested {
public int doStuff(int size) {
size++; // 局部变量size
this.size++; // 嵌套类Nested的成员变量
OuterNested3.this.size++;// 外部类OuterNested3 的成员变量
return
((size++)+(this.size++)+(OuterNested3.this.size++)); }
// TestOuterNested3.java
public class TestOuterNested3 {
public static void main(String[] args) {
OuterNested3 outer = new OuterNested3();
OuterNested3.Nested nested = outer.new Nested();
System.out.println(nested.doStuff(1));