java - Implement interface in Fragment

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65649880/implement-interface-in-fragment

Answer 1

You get the NullPointerException because you did not assign anything to the newInterface property in your ClassX object.

I don't understand why you call classx.sum(1,1); while your sum method on ClassX doesn't accept any parameters.

Try this:
Create a constructor for your ClassX which takes a NewInterface parameter. So your ClassX would look like this:

public class ClassX {

private NewInterface newInterface;

public ClassX(NewInterface newInterface) {
    this.newInterface = newInterface;
}

public void sum(){

    newInterface.sum(1,1);

}

}

and then initialize your classX object like this:

classX = new ClassX(this);

before calling

classX.sum();