内部类

public class Outer {
    private int x=3;
    
    class Inner{
        void function(){
            System.out.println("inner"+x);
        }
    }
    
    void method(){
        Inner in=new Inner();
        in.function();
    }
}

public class Test {

    public static void main(String[] args) {
        //直接访问内部类中的成员
        Outer.Inner in=new Outer().new Inner();
        in.function();
    }

}