Change value of a local variable that needs to be declared final

Question

I have been trying to change the position of my JButton in the action listener. However, when I compiled my code Local variable is accessed from within inner class: needs to be declared final error was displayed. Therefore, I declared my location variable as final. The problem is that I need to change the value of my location variable and that is not possible as long as its final. How do I solve this?

Code:

final int location =100;

JFrame f = new JFrame();
final JButton b1 = new JButton("character");

f.setVisible(true);
f.setSize(500,500);
f.setDefaultCloseOperation(EXIT_ON_CLOSE);
f.setLocationRelativeTo(null);
f.setLayout( new FlowLayout());

f.add(b1);

b1.addActionListener(new ActionListener() {     
  public void actionPerformed(ActionEvent e) {
     b1.setLocation(location,100);
     location += 10; // cannot assign a value to final variable location
  }
});

Answer 1

You can do it in two ways,

1) Implement ActionListener to your parent class then in

ParentClass implements ActionListener 
{
int location =100;
 //...Codes codes..
 public void actionPerformed(ActionEvent e) {
 //perform null check 
  if (b1==(JButton)e.getSource()){
   b1.setLocation(location,100);
    location += 10;

    }
  }
}

2) Call static variables from inner class, (remember: This is a bad method of programming)

 //static class to store variables
  Class StaticVariables{
  static int location=100;
 }



class ParentClass{

    //..Codes Codes..

    b1.addActionListener(new ActionListener() {
    //Calling Static class varible
    int localLocationVariable=StaticVariables.location;
    b1.setLocation(localLocationVariable,100);
    localLocationVariable+= 10;
    StaticVariables.location=localLocationVariable;
    }

Hopes this may help you.