嵌套类 内部类 静态内部类 匿名内部类
一、嵌套类（Nested Class）分为:内部类（Inner Class）、静态嵌套类（Static Nested Class）
二、写法:
class OutClass{
??? static class?StaticNestedClass{
??????? ...
??? }
??? class InnerClass{
??????? ...
??? }
}
?
三、为什么要用嵌套类：
1、当仅希望在某个类中使用一个类时，用嵌套类的写法，就起到封装的作用。
2、提高代码可读性，与可维护性。
?
四、用例：
public class DataStructure {
??? private final static int SIZE = 15;
??? private int[] arrayOfInts = new int[SIZE];
???
??? public DataStructure() {
??????? for (int i = 0; i < SIZE; i++) {
??????????? arrayOfInts[i] = i;
??????? }
??? }
???
??? public void printEven() {
??????? InnerEvenIterator iterator = new InnerEvenIterator();//外部类中直接调用内部类
??????? while (iterator.hasNext()) {
??????????? System.out.println(iterator.getNext() + " ");
??????? }
??? }
???
??? private class InnerEvenIterator {//非静态内部类
??????? private int next = 1;
??????? public boolean hasNext() {
??????????? return (next <= SIZE - 1);
??????? }
???????
??????? public int getNext() {
??????????? int retValue = arrayOfInts[next];//直接访问外部类变量
??????????? next += 2;
??????????? return retValue;
??????? }
??? }
????
??? private void outPrivateFunction(){}
??? private static void staticOutPrivateFunction(){}
??? private static int i;
??? static class NestedClass//静态嵌套类
??? {? ?
??? ?NestedClass(){}
??? ?int i = 8;
??? ?void access()
??? ?{
??? ??System.out.println(i);//自身变量的访问
??????System.out.println(DataStructure.i);//外部类变量的访问
??? ??DataStructure.staticOutPrivateFunction();//调用外部类静态方法
??? ??new DataStructure().outPrivateFunction();
?????}
??? }
???
??? interface Work //接口也可作为嵌套类，实现匿名嵌套类，参数嵌套类类似
??? {
??? ?public int Money();
??? }
???
??? public static void main(String s[]) {
??? ?DataStructure.InnerEvenIterator ie = new DataStructure().new InnerEvenIterator(); //创建非静态内部类实例
?????DataStructure.NestedClass dn = new DataStructure.NestedClass(); //创建静态嵌套类实例
??? ?DataStructure ds = new DataStructure();
??? ?ds.printEven();
?????dn.access();
??? ?new Work()
??????? {
??????? ?public int Money(){ return 2000;};
??????? }.Money();
??? }
}
