我如何从内部类对象访问外部类的方法和全局变量，如果我不能实现内部类的目的?

public class StaticAndInnerClasses {
    String testString;
    class InnerClass{
    int x;
    int y;


    }
    static class InnerStaticClass{
    int a=10;
    int b=20;

    }
    public void changeCharacter(){
    testString="Characters modified";
    }
    public static void main(String[] args){
    StaticAndInnerClasses.InnerStaticClass statciClassObject=new StaticAndInnerClasses.InnerStaticClass();
    StaticAndInnerClasses outerObject=new StaticAndInnerClasses();
    outerObject.changeCharacter();
    InnerClass innerClassObject=outerObject.new InnerClass();    
    innerClassObject.changeCharacter();   



  }
    }

As you can see in my code that I have created a innerClassObject in the last line, now I want to know why I am not able to access the String testString using innerClassObject. isn't testString a Global variable and haven't I created the instance of innerClass within the outerClass .i.e "StaticAndInnerClasses" And if it is not possible then why have the Inner Classes

正如您在我的代码中看到的，我在最后一行中创建了一个innerClassObject，现在我想知道为什么我不能使用innerClassObject访问字符串testString。testString不是全局变量，我没有在outerClass中创建innerClass的实例。如果不可能的话，为什么要有内部类。

2 个解决方案

#1

Code inside the inner class can reference the stuff in the outer class.

内部类中的代码可以引用外部类中的内容。

For this toy example:

这个玩具的例子:

public class StaticAndInnerClasses {
    String testString;
    class InnerClass{
        int x;
        int y;

        public void printString() {
            changeCharacter();
            System.out.println(testString);
        }
    }

    static class InnerStaticClass{
        int a=10;
        int b=20;

    }
    public void changeCharacter(){
        testString="Characters modified";
    }

    public static void main(String[] args){
        StaticAndInnerClasses.InnerStaticClass statciClassObject=new StaticAndInnerClasses.InnerStaticClass();
        StaticAndInnerClasses outerObject=new StaticAndInnerClasses();
        StaticAndInnerClasses.InnerClass innerClassObject=outerObject.new InnerClass();
        innerClassObject.printString();

    }
}

So in the code of the inner class, you can reference methods and fields of the outer class, as is done here in the method printString(). This does not turn the outer class methods into methods of the inner class so the code (in the outer class main)

因此，在内部类的代码中，可以引用外部类的方法和字段，就像在方法printString()中所做的那样。这并没有将外部类方法转换为内部类的方法，因此代码(在外部类main中)

innerClassObject.changeCharacter();

as you referenced in a comment, will not work. It in fact won't compile.

正如您在评论中所引用的，将不起作用。它实际上不会编译。

#2

There's a difference between an inner class and a static inner class.

内部类和静态内部类之间有区别。

A static inner class is not associated with any instance of the outer class, hence why you can't access the enclosing classes' fields.

静态内部类与外部类的任何实例都没有关联，因此为什么不能访问封闭类的字段。

However, a non-static inner class must be constructed using an instance of the outer class. So, your test code would look like:

但是，必须使用外部类的实例构造非静态的内部类。因此，您的测试代码如下所示:

OuterClass outer = new OuterClass();
InnerClass inner = outer.new InnerClass();//Yes, with that exact syntax!

EDIT For those saying the above does not compile, here's the exact message from Eclipse when trying to instantiate InnerClass directly:

编辑那些说上面没有编译的内容，这里是在尝试直接实例化InnerClass时从Eclipse得到的确切消息:

No enclosing instance of type OuterClass is accessible. Must qualify the allocation with an enclosing instance of type OuterClass(e.g. x.new A() where x is an instance of OuterClass).

没有可访问类型OuterClass的封闭实例。必须用类的封闭实例来限定分配(例如:x。新A()，其中x是一个OuterClass实例。

#1