Java 中的静态嵌套类和非静态嵌套类

Java 中的静态嵌套类和非静态嵌套类

术语:嵌套类分为两类:静态嵌套类和非静态嵌套类.声明 static 的嵌套类称为静态嵌套类,非静态嵌套类也称为内部类.

class OuterClass {
    private static String msg = "GeeksForGeeks";

    public static class NestedStaticClass {
        public void printMessage() {
            System.out.println("Message from nested static class: " + msg);
        }
    }

    public class InnerClass {
        public void display() {
            System.out.println("Message from non-static nested class: " + msg);
        }
    }
}

public class Main {
    public static void main(String args[]) {
        OuterClass.NestedStaticClass printer = new OuterClass.NestedStaticClass();
        printer.printMessage();

        OuterClass outer = new OuterClass();
        OuterClass.InnerClass inner = outer.new InnerClass();
        inner.display();

        OuterClass.InnerClass innerObject = new OuterClass().new InnerClass();
        innerObject.display();
    }
}

运行结果

```
Message from nested static class: GeeksForGeeks
Message from non-static nested class: GeeksForGeeks
Message from non-static nested class: GeeksForGeeks
```

public class ShadowTest {

    public int x = 0;

    class FirstLevel {

        public int x = 1;

        void methodInFirstLevel(int x) {
            System.out.println("x = " + x);
            System.out.println("this.x = " + this.x);
            System.out.println("ShadowTest.this.x = " + ShadowTest.this.x);
        }
    }

    public static void main(String... args) {
        ShadowTest st = new ShadowTest();
        ShadowTest.FirstLevel fl = st.new FirstLevel();
        fl.methodInFirstLevel(23);
    }
}

运行结果

```
x = 23
this.x = 1
ShadowTest.this.x = 0
```

参考资料

• https://docs.oracle.com/javase/tutorial/java/javaOO/nested.html
• https://www.geeksforgeeks.org/static-class-in-java/