Java内部类（Inner Class）详解

简单的说，内部（inner）类指那些类定义代码被置于其它类定义中的类；而对于一般的、类定义代码不嵌套在其它类定义中的类，称为顶层（top-level）类。对于一个内部类，包含其定义代码的类称为它的外部（outer）类。 1          Static member class（静态成员类） 类声明中包含“static”关键字的内部类。如以下示例代码， Inner1/Inner2/Inner3/Inner4就是Outer的四个静态成员类。静态成员类的使用方式与一般顶层类的使用方式基本相同。
public class  Outer{
    //just like static method, static member class has public/private/default access privilege levels

    //access privilege level: public
    public static class Inner1 {
        public Inner1() {
            //Static member inner class can access static method of outer class
            staticMethod();
            //Compile error: static member inner class can not access instance method of outer class
            //instanceMethod();
        }
    }

    //access privilege level: default
    static class Inner2 {

    }

    //access privilege level: private
    private static class Inner3 {
        //define a nested inner class in another inner class
        public static class Inner4 {
        }
    }

    private static void staticMethod() {
        //cannot define an inner class in a method
        /*public static class Inner4() {
        }*/
    }

    private void instanceMethod() {
        //private static member class can be accessed only in its outer class definition scope
        Inner3 inner3 = new Inner3();
        //how to use nested inner class
        Inner3.Inner4 inner4 = new Inner3.Inner4();

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