NullPointerException received trying to change the button label

[Douglas Walters]

I'm getting a java.lang.NullPointerException error during runtime when trying to change the button text when clicking the button, eastButton (line 46). I placed a System.out.println statement and the text print with no errors, so I know the coding is correct (with the exception to the setLabel command).
Any ideas?
Thanks

Doug

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

public class Button3 
{
	
	JButton eastButton;
	
	public static void main(String [] arga)
	{
		Button3 gui = new Button3();
		gui.go();
	}  //  End main
	
	public void go()
	{
		JFrame frame = new JFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		JButton eastButton = new JButton("East");
		eastButton.addActionListener(new eastListener());
		JButton west = new JButton("West");
		JButton north = new JButton("North");
		JButton south = new JButton("South");
		JButton center = new JButton("Center");
		
		frame.getContentPane().add(BorderLayout.EAST, eastButton);
		frame.getContentPane().add(BorderLayout.WEST, west);
		frame.getContentPane().add(BorderLayout.NORTH, north);
		frame.getContentPane().add(BorderLayout.SOUTH, south);
		frame.getContentPane().add(BorderLayout.CENTER, center);
		
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(300, 300);
		frame.setVisible(true);
	}  // End go()
	
	class eastListener implements ActionListener
	{
		public void actionPerformed(ActionEvent event)
		{
			try 
			{
				eastButton.setLabel("Not West!");	
			}
			catch (Exception ex)
			{
				System.out.println(ex);
			}	
		}  //  End actionPerformed ()

	}  //  End class eastListener()
}  //  End class Button3
   

[Ankit Garg]

line number 23 i.e. JButton eastButton = new JButton("East"); is creating the problem. This a local declaration which hides the class field eastButton. Change the statement to

eastButton = new JButton("East");

[Douglas Walters]

Thanks Ankit

This worked. I'm currently going through the Heads Up book and an example they used only displayed the buttons, but no action was attached to them. I went a step foward and added the action, but didn't realize that the JButton within the method over wrote the class button. Thanks again for your help...Doug

[Ankit Garg]

It's good to experiment with the things Douglas ...