Tukukkk

I'm having problems settings my JTextField from another class. When i press button "=" it is supposed to do calculations inside AddNumbers class and set JTextField as result of calculations. But for now it is throwing NullPointerException. I can't figure out how to set up JTextField. I have to set it inside AddNumbers due to Chain of Responsibilities Design.

public class AddNumbers implements Chain {

private Chain nextInChain;

public CalcGui calcgui;

int result=0;



@Override

public void setNextChain(Chain nextChain) {

    // TODO Auto-generated method stub

    this.nextInChain=nextChain;

}



@Override

public void calculate(Numbers request) {

    // TODO Auto-generated method stub

    if(request.GetCalcWanted()=="add") {

        result = request.GetNumber1()+ request.GetNumber2();

        this.calcgui.txtWynik.setText(String.valueOf(result)); //NULLPOINTER

    }else {

        nextInChain.calculate(request);

    }

}

And here is CalcGui class

public class CalcGui {



private JFrame frame;

JTextField txtWynik; 

static Numbers request;

int x,y;

String operation;

boolean clicked = false;

/**

 * Launch the application.

 */

public static void main(String args) {

    EventQueue.invokeLater(new Runnable() {

        public void run() {

            try {

                CalcGui window = new CalcGui();

                window.frame.setVisible(true);





            } catch (Exception e) {

                e.printStackTrace();

            }

        }

    });

}



/**

 * Create the application.

 */

public CalcGui() {

    initialize();

}



/**

 * Initialize the contents of the frame.

 */

private void initialize() {

    frame = new JFrame();

    frame.setBounds(100, 100, 270, 361);

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.getContentPane().setLayout(null);



    txtWynik =new JTextField();

    Chain chainCalc1=new AddNumbers();    

    JButton btneq = new JButton("=");

    btneq.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {

            request = new Numbers(x,y,operation);

            chainCalc1.calculate(request);



        }

    });

I will give you one idea, this method:

public void calculate(Numbers request) {

Could receive the reference to your JTextField, like this:

public void calculate(Numbers request,JTextField out) {

    if(request.GetCalcWanted().equals("add")) {

        result = request.GetNumber1()+ request.GetNumber2();

        out.setText(String.valueOf(result)); //NO NULLPOINTER SINCE YOU PASS PARAMETER

    }else {

        nextInChain.calculate(request);

    }

}

I think that solve your NPE issue.

Cheers,

-Rod