calling method gives an error of non-static method

Question

I have a method name MakeKK

public void MakeKK(String K1, String K2){
    ....
 }

I try to call this method in this following way,

File f = null;

MakeKK(f.getAbsolutePath()+ "\\Text.txt", f.getAbsolutePath()+"\\Text2.txt");  

But it gives an error of

Error: non-static method MakeKK

Can anyone spot my mistake?

Answer 1

If you are calling MakeKK from main(), you have 3 options

1. Make MakeKK static..
2. Create an instance of class containing MakeKK and use the instance to call MakeKK.
3. You will get NullPointerException when you run your code as f is null..

Answer 2

You have to create an instance of the class that "contains" the MakeKK() method.

File f = null;
// ... Here you may add some code to avoid NullPointerException
NameOfClass obj = new NameOfClass(...);
obj.MakeKK(...); 

so you use it to call that method.

Another solution would be making the method static:

public static void MakeKK(String K1, String K2){
    ....
}

Choosing the correct way depends on what you are doing in the program, and what your method MakeKK() does. You could read this SO post in order to understand when to use static methods.

Notes:

• You are initializing File f with null, which would lead into a NullPointerException when you call the method MakeKK(...)
• I would recommend you to follow Java naming conventions. You should call your method something like: nameOfMethod instead of NameOfMethod. This last is used when naming classes, interfaces... Your method should be called makeKK().