内部类（2）

内部类的继承

1.内部类的继承与外围类的继承类似

class A{ void f1(){ System.out.println("A.f1()"); } } public class Outer{ class Inner extends A{ } public static void main(String[] args){ Outer a = new Outer(); Inner inner = a.new Inner(); inner.f1(); } } //运行结果： //ly@HP:~/TIJ4/exercise$ javac Outer.java //ly@HP:~/TIJ4/exercise$ java Outer //A.f1()

2.内部类可以被继承,但父类和子类都需要外围类的实例

内部类的子类构造器需要指定父类的外围类实例作为参数，否则子类无法对父类进行初始化

class Outer1{ class Inner1{ Inner1(){System.out.println("Outer1.Inner1");} } } public class Outer{ class Inner extends Outer1.Inner1{ //Inner(){} //编译错误，需要一个父类的外围类实例 Inner(Outer1 a){ a.super(); System.out.println("Outer.Inner"); } } public static void main(String[] args){ Outer a = new Outer(); Outer1 a1= new Outer1(); Inner b = a.new Inner(a1); } } //运行结果： //ly@HP:~/TIJ4/exercise$ javac Outer.java //ly@HP:~/TIJ4/exercise$ java Outer //Outer1.Inner //Outer.Inner

3.外部类的子类重定义一个相同名字的内部类，基类的内部类不会被覆盖，两个类是独立的个体，没有出现动态绑定

class Base{ class Inner{ Inner(){System.out.println("Base.Inner");} } } public class Outer extends Base{ class Inner{ Inner(){System.out.println("Outer.Inner");} } public static void main(String[] args){ Base a = new Outer();//将子向上转型为父类 Base.Inner b = new a.new Inner();//调用父类的Inner构造器，而不是子类 //Outer.Inner b = a.new Inner(); //Base.Inner不可以被转换成Outer.Inner } } //运行结果： //ly@HP:~/TIJ4/exercise$ javac Outer.java //ly@HP:~/TIJ4/exercise$ java Outer //Base.Inner

4.如果没有在子类中覆盖父类的内部类，则父类中的内部类也会被继承到基类中

class Base{ class Inner{ Inner(){System.out.println("Base.Inner");} } } public class Outer extends Base{ /* class Inner{ Inner(){System.out.println("Outer.Inner");} } */ public static void main(String[] args){ Outer a = new Outer(); Inner b = a.new Inner();//调用父类的Inner构造器 } } //运行结果： //ly@HP:~/TIJ4/exercise$ javac Outer.java //ly@HP:~/TIJ4/exercise$ java Outer //Base.Inner

5.修改上面的代码，验证动态绑定只对函数有效，对内部类无效

class Base{ void f1(){ System.out.println("Base.f1()"); } class Inner{ Inner(){ System.out.println("Base.Inner"); f1(); } } } public class Outer extends Base{ void f1(){ System.out.println("Outer.f1()"); } class Inner{ Inner(){ System.out.println("Outer.Inner"); f1(); } } public static void main(String[] args){ Base a = new Outer(); Base.Inner b = a.new Inner();//子类调用父类的内部类构造器，调用子类的f1()方法。 } } //运行结果 //ly@HP:~/TIJ4/exercise$ javac Outer.java //ly@HP:~/TIJ4/exercise$ java Outer //Base.Inner //Outer.f1()

内部类的作用

使用同一个接口，实现同一个函数不同的功能，与多态结合

interface Interface1{ void f1(); } public class LightControl{ class LightOn implements Interface1{ public void f1(){ System.out.println("light on"); } } class LightOff implements Interface1{ public void f1(){ System.out.println("ligth off"); } } public static void main(String[] args){ LightControl a = new LightControl(); Interface1 lightOn = a.new LightOn();//创建开灯实例，向上转型为父类 Interface1 lightOff = a.new LightOff();//创建关灯实例，向上转型为父类 lightOn.f1(); lightOff.f1(); } } //运行结果： //ly@HP:~/TIJ4/exercise$ javac LightControl.java //ly@HP:~/TIJ4/exercise$ java LightControl //light on //ligth off