NullPointerException occured

[Ben Hultin]

I did some research on my exception I found, but I cant figure out how to solve the issue.

my error:

C:\Documents and Settings\ben\Desktop\park>java BenHultinProg7
Exception in thread "main" java.lang.NullPointerException
at Prog7.<init>(Prog7.java:32)
at BenHultinProg7.main(BenHultinProg7.java:12)

C:\Documents and Settings\ben\Desktop\park>

here is my driver class:

   import javax.swing.JFrame;



public class BenHultinProg7 {

	String[] colors = {"red", "white", "yellow", "green", "blue"};


	public static void main(String [] args) {
		
		Prog7 progObj = new Prog7();
		progObj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		progObj.setSize(300, 100);
		progObj.setVisible(true);
		
		
		
	} // end main method
		
} // end BenHultinProg7 class		
 

here is my driven class:

 

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;



public class Prog7 extends JFrame{
	
	private JOptionPane outPut;
	private String message;
	private JTextField field1;
	private JTextField field2;
	private JTextField field3;
	private JTextField field4;
	private JTextField field5;
	private JButton button;
	private FlowLayout layout;

	public Prog7() {
		// sets windows title
		super("the title");
		layout = new FlowLayout();
		// sets the default layout to the FlowLayout manager
		setLayout(layout);
	
		TheHandler handler = new TheHandler();
		field1.addActionListener(handler);
		field2.addActionListener(handler);
		field3.addActionListener(handler);
		field4.addActionListener(handler);
		field5.addActionListener(handler);
		
		button = new JButton("OK");
		add(button);
		
		outPut = new JOptionPane();
		add(outPut);
	
	} // end Prog7() constructor
	
	private class TheHandler implements ActionListener {
	
		public void TheHandler() { }
	
		public void actionPerformed(ActionEvent event) {
		
			String string = "";
			if (event.getSource() == field1) {
				// getActionCommand() gets the string value from field 1 and make it equal to %s
				string = String.format("field 1: %s", event.getActionCommand());
				
					if (string.equalsIgnoreCase("red")) {
						
						JOptionPane.showMessageDialog(null, congratsMessage());
					} else {
						JOptionPane.showMessageDialog(null, sorryMessage());
					}
				
			} else if (event.getSource() == field2) {
				string = String.format("field 2: %s", event.getActionCommand());
				
					if (string.equalsIgnoreCase("white")) {
						JOptionPane.showMessageDialog(null, congratsMessage());
					} else {
						JOptionPane.showMessageDialog(null, sorryMessage());
					}
				
			} else if (event.getSource() == field3) {
				string = String.format("field 3: %s", event.getActionCommand());
				
					if (string.equalsIgnoreCase("yellow")) {
						JOptionPane.showMessageDialog(null, congratsMessage());
					} else {
						JOptionPane.showMessageDialog(null, sorryMessage());
					}
					
			} else if (event.getSource() == field4) {
				string = String.format("field 3: %s", event.getActionCommand());
				
					if (string.equalsIgnoreCase("green")) {
						JOptionPane.showMessageDialog(null, congratsMessage());
					} else {
						JOptionPane.showMessageDialog(null, sorryMessage());
					}
					
			} else if (event.getSource() == field5) {
				string = String.format("field 3: %s", event.getActionCommand());
				
					if (string.equalsIgnoreCase("blue")) {
						JOptionPane.showMessageDialog(null, congratsMessage());
					} else {
						JOptionPane.showMessageDialog(null, sorryMessage());
					}
			}
		
		} // end actionPerformed() method 
		
		public String sorryMessage() {
			message = "Sorry, but you didnt choose the right color.";
			return message;
		}
		
		public String congratsMessage() {
			message = "Congratulations! You got all the colors correct.";
			return message;
		}
	
	} // end inner class

} // end Prog7 class
   

Thanks a lot for the help

[Rob Spoor]

The NPE says exactly which line is causing it:

at Prog7.<init>(Prog7.java:32)

Line 32 of Prog7.java. In this case, it's

field1.addActionListener(handler);

The reason? You never assign anything to field1. Or any of the other fields, for that matter.

[Christiaan Lombard]

Fix:

  
field1 = new JTextField();
field2 = new JTextField();
field3 = new JTextField();
field4 = new JTextField();
field5 = new JTextField();

Add this right before:

field1.addActionListener(handler);