1.内部类，在一个类中置入另一个类，可以起到隐藏类的作用。通常的内部类设计中，会返回内部类的引用。
Exercise01
package innerclass; public class Outer { class Inner{ private int step; Inner(int i){ step = i; } int get_step() { return step; } } public Inner get_inner(int i) { return new Inner(i); } public static void main(String[] args) { Outer o = new Outer(); o.get_inner(3).get_step(); } }
2.内部类可以访问外部类的所有玩意。
Exercise03
package innerclass; public class Sequence { private String ss; Sequence(String s){ ss = s; } private class display{ public String toString() { return ss; } } public display re_display() { return new display(); } public static void main(String[] args) { Sequence s = new Sequence("I am your father"); display d = s.re_display(); System.out.println(d.toString()); } }
3.如果内部类中需要外部类的引用，那么用Outer class.this。如果想要直接在main里创建内部类的对象，必须使用Outer classs.new。
4.非内部类不能声明为private或protected。一旦内部类声明为protected，不同包就算继承外部类也无法访问。内外部类可以互相访问private方法以及数据域。
Exercise07
package innerclass; class EX06{ private int ex; private int get_ex() { return ex; } private void call_inner() { Inner i = new Inner(); i.modi(); } class Inner{ private void modi() { ex = 1; System.out.println(get_ex()); } } public static void main(String[] args) { EX06 e = new EX06(); e.call_inner(); }}
5.可以在方法中直接置入内部类，不需要单独分成两部分。
package innerclass; public class EX09 { public Inter1 re_inter1() { class Inter implements Inter1{ private int x; public void atleast() { System.out.println("Inter" + "(" + x + ")"); } } return new Inter(); } public static void main(String[] args) { EX09 e = new EX09(); Inter1 i = e.re_inter1(); i.atleast(); } }
6.对象要在匿名内部类使用必须时final，但是如果是构造器内使用则不需要final。只能implement一个接口。不能同时继承一个类和继承一个接口。
Exercise13
package innerclass; public class Ex13 { public Inter1 inter() { return new Inter1() { private int x; public void atleast() { System.out.println("Inter"); } }; } public static void main(String[] args) { Ex13 e = new Ex13(); Inter1 i = e.inter(); i.atleast(); } }
Exercise15
package innerclass; public class Ex15 { public First f() { return new First() { {System.out.println("instance initializer");} //must be embraced by braces }; } public static void main(String[] args) { Ex15 e = new Ex15(); e.f(); } } class First{ private int x; First(int i){ x = i; } First(){ x = 1; System.out.println("no argument"); } } class Second{ First f() { return new First(); } }
7.结合以下的例子，体会用匿名函数创建工厂函数。
Exercise16
package innerclass; public class Ex16 { public static void get(WheelFactory factory) { Cycle c = factory.getCycle(); c.wheels(); } public static void main(String[] args) { get(Unicle.wheel); get(Tricycle.wheel); get(Bicycle.wheel); } } class Unicle implements Cycle{ public void wheels() { System.out.println("Unicle"); } public static WheelFactory wheel = new WheelFactory() { public Cycle getCycle() { return new Unicle(); } }; } class Bicycle implements Cycle{ public void wheels() { System.out.println("Bicycle"); } public static WheelFactory wheel = new WheelFactory() { public Cycle getCycle() { return new Bicycle(); } }; } class Tricycle implements Cycle{ public void wheels() { System.out.println("Tricycle"); } public static WheelFactory wheel = new WheelFactory() { public Cycle getCycle() { return new Tricycle(); } }; }
Exercise17
package innerclass; import java.util.*; public class Ex17 { public static void get(Factory factory) { Toss t = factory.get_Toss(); t.display(); } public static void main(String[] args) { get(Coin.factory); get(Dice.factory); } } class Coin implements Toss{ private int i; Coin(){ Random rand = new Random(); i = rand.nextInt(2); } public void display() { switch(i) { case 0:System.out.println("you got positive"); break; case 1:System.out.println("you got negetive"); } } public static Factory factory = new Factory() { public Toss get_Toss() { return new Coin(); } }; } class Dice implements Toss{ private int i; Dice(){ Random rand = new Random(); i = rand.nextInt(6); } public void display() { switch(i) { case 0:System.out.println("you got 1"); break; case 1:System.out.println("you got 2"); break; case 2:System.out.println("you got 3"); break; case 3:System.out.println("you got 4"); break; case 4:System.out.println("you got 5"); break; case 5:System.out.println("you got 6"); } } public static Factory factory = new Factory() { public Toss get_Toss() { return new Dice(); } }; }
8.nested class意思即内部类为static，与外部类没有任何联系也不会有外部类的引用。意味着创建内部类的对象不需要外部类，同时，无法访问外部类的非static对象。我们也可以在接口里置入nested class（因为接口默认其中的类是public static）。
Exercise20
package innerclass; public class Ex20 implements Nested{ public static void main(String[] args) { Test t = new Test(); //static class created without outer class object t.test(); } }
Exercise21
package innerclass; public interface Nested { void howdy(); public static class Test{ public static void test(Nested n) { n.howdy(); System.out.println("Test.test()"); } } } // package innerclass; public class Ex20 implements Nested{ public void howdy() { System.out.println("Nested.howdy()"); } public static void main(String[] args) { Ex20 e = new Ex20(); Test.test(e); } }
9.内部类可以拥有多个实例，特别是当你要同时要继承两个非接口类的时候，只能用内部类。
原文：https://www.cnblogs.com/waytek/p/11259513.html