无法从子类访问方法

Question

I'm just trying to use Method_In_SubClass() method from SubClass Class but I'm getting these errors. I tried by changing Method_In_SubClass to Static but still getting errors

public class Sub {

//Method 1 : Non-Static
public void  nonstatictest(){
    System.out.println("This is non-Static method.");
}

//Mehod 2 : Static
public static void statictest(){
    System.out.println("This is static method.");
}

//SubClass 
public class SubClass{

    //Method in SubClass
    public void Method_In_SubClass(){
            System.out.println("This is Method in SubClass");
    }
}


public static void main(String args[]){
        Sub SubObject = new Sub();
        SubClass SubClassobject = new SubClass();
        SubObject.nonstatictest();
        statictest();
        SubClassobject.Method_In_SubClass();

}
}

Error:

Sub.java:25: error: non-static variable this cannot be referenced from a static context
            SubClass SubClassobject = new SubClass();
                                        ^
1 error

Then I changed Method_In_SubClass to static but getting this error

Error :Illegal static declaration in inner class Sub.SubClass
        public static void Method_In_SubClass(){
                           ^
  modifier 'static' is only allowed in constant variable declarations
Sub.java:25: error: non-static variable this cannot be referenced from a static context
            SubClass SubClassobject = new SubClass();

Answer 1

Both Main and SubClass are members of class Sub and you cannot reference a non-static member of class sub that is SubClass in Main which is a static member. You need make the entire SubClass into static instead of just the Method_In_SubClass().

Answer 2

The Easiest way to make it work is by making SubClass as Static

 public static class SubClass{

    //Method in SubClass
    public void Method_In_SubClass(){
            System.out.println("This is Method in SubClass");
    }
}

I assumed that initiating SubClass Object/Instance of the class would be same as Parent class but it's not

SubClass SubClassobject = new SubClass();

The correct way of initiating an object of the subclass is:

Sub.SubClass SubClassobject = SubObject.new SubClass();