Call function in stateChanged()

Question

I got class A which, after button is clicked:

if (source == buttonA){          
new classB(this);
}

moreover, class A has function named

function(int a);

In class B I've got

public class classB extends JFrame implements ChangeListener {    

    public classB(A a) {
        public void stateChanged(ChangeEvent e){            
           JSlider source = (JSlider)e.getSource();
           tmp = source.getValue();                             
           a.function(tmp);         
        }
    }
}

But a cannot be resolved. How can I achieve that in other way?

Answer 1

You should change classB to this:

  public class classB extends JFrame implements ChangeListener {
    private A a;

    public classB(A a) {
      this.a = a;
    }

    public void stateChanged(ChangeEvent e) {
      JSlider source = (JSlider)e.getSource();
      int tmp = source.getValue();
      a.function(tmp);
    }
  }

Explanation

A couple of things were wrong with this class. Firstly the nested stateChanged function in the constructor. Taking this out, meant that classB needed a reference to class A , that's why it needed a private A a; field, and needed to be set in the constructor. Also, variable tmp was not declared, always declare a variable before using it.

using this would have worked as well:

int tmp;                    //<-- variable declared, you can now assign a value to it.
tmp = source.getValue();