java runtime exception help

EyeSight

hey guys, here's a watered down version of my code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;


public class Test implements ActionListener{
    public static JTextField leftField;
    public static JTextField rightField;
    public JPanel panel;
    public JButton plus;
    public JButton clear;
    
    public static void main(String[] args) {
        Test test = new Test();
     }
     
    private Test(){
        JFrame frame = new JFrame("Calculator");
        JPanel fieldPanel = new JPanel();
        panel = new JPanel();
        
        frame.getContentPane().add(BorderLayout.NORTH, fieldPanel);
        frame.getContentPane().add(BorderLayout.CENTER, panel);
            
        fieldPanel.add(leftField);
        fieldPanel.add(rightField);
            
        plus = new JButton("+");
        panel.add(plus);
        plus.addActionListener(this);
        
        clear = new JButton("CE");
        panel.add(clear);
        clear.addActionListener(this);
        
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 200);
        frame.setVisible(true);
    }
    
    public void actionPerformed(ActionEvent event){
        leftField.setText("worked");
    }
}

and here's the error i'm getting:

Exception in thread "main" java.lang.NullPointerException
        at java.awt.Container.addImpl(Container.java:1066)
        at java.awt.Container.add(Container.java:377)
        at Test.<init>(Test.java:25)
        at Test.main(Test.java:14)

so basically the line:
" Test test = new Test();"
in my main method is causing the problem. can anybody tell me why? i've googled it with no success and i have used this method before when coding and never had this problem!

Joneser

Hi EyeSight, I think the problem is that you aren't initialising your JTextField variables. Try doing

rightField = new JTextField();
leftField = new JTextField();

before you add them to your JPanel.

Good Luck

Edit: Remember not to just look at the bottom line number in your error, I only figured this out because of the one above it pointing to line 25.