如何从嵌套类访问Extended Class的方法？

Question

I have two nested classes inside a class with the outer class extending another class. The structure is something like this.

public class EXTENSION_CLASS
{
    public int Get_Value()
    {
        return(100);
    }
}

public class OUTER extends EXTENSION_CLASS
{
    public static class NESTED1
    {
        public void Method1()
        {
          int value=0;
          value=Get_Value();
          System.out.println("Method1: "+value);
        }
    }
    public static class NESTED2
    {
        NESTED1 Nested1_Instance=new NESTED1();
        public void Method2()
        {
            Nested1_Instance.Method1();
        }
    }
    public void run()
    {
        NESTED2 Nested2_Instance=new NESTED2();
        Nested2_Instance.Method2();
    }
    public static void main (String[] args)
    {
       OUTER New_Class=new OUTER();
       New_Class.run();
    }
}

I'm expecting the output: "Method1: 100". But, am getting the output: "OUTER.java:16: error: non-static method Get_Value() cannot be referenced from a static context value=Get_Value();". How can i make this working?

Cheers !

Rajesh.

Answer 1

从NESTED1和NESTED2的声明中删除static修饰符，如下所示：

public class NESTED1

Answer 2

You're trying to make a static reference to a non-static member.

This means that you're trying to access a instance member from a static member of the class.

To fix the issue, remove the static modifier from both the NESTED1 and NESTED2 clases.

Alternately, if you do not wish to remove the static modifier, you will have to create an object of the OUTER or EXTENSION_CLASS classes and then invoke Get_Value() using the object.

For example:

public void Method1()
{
      int value=0;
      EXTENSION_CLASS ext = new EXTENSION_CLASS ();
      value=ext.Get_Value();
      System.out.println("Method1: "+value);
}

OR

public void Method1()
{
      int value=0;
      OUTER outer = new OUTER();
      value=outer.Get_Value();
      System.out.println("Method1: "+value);
}

Answer 3

If you want keep the nested classes static, you will have to create an instance of OUTER in the Method1() to access Get_Value().

  public void Method1()
    {
      int value=0;
       OUTER outer = new OUTER();
       value=outer.Get_Value();
      System.out.println("Method1: "+value);
    }

Answer 4

The error says every thing. You can not call non-static methods from static methods / class. To make it work, Simply add static keyword to 'Get_Value' method in EXTENSION_CLASS.