Java Technology Forums - Changin JButton Icons via action performed

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문의내용

Hi, I have been fiddling with this for some time with no result I was wondering if anyone could tell me how to do this

Basically I have an action listener in another class that is supposed to change the colour of the buttons when it is pressed, below is the code for the action performed method. I have tried revalidate and repaint in various ways but keep getting a null pointer exception, please help:

public void actionPerformed(ActionEvent e) 
{ 
forwardButton.setIcon(newImageIcon("images/forwardButtonBlue.jpg"));

stopButton.setIcon(new ImageIcon("images/stopButtonBlue.jpg "));

backButton.setIcon (new ImageIcon("images/backButtonBlue.jpg"));

magButton.setIcon (new ImageIcon("images/magnifyButtonBlue.jpg"));

homeButton.setIcon (new ImageIcon("images/homeButtonBlue.jpg"));

refreshButton.setIcon(new ImageIcon("images/refreshButtonBlue.jpg"));
}

답변내용  

5 helpful answers below.

 

Sat, 14 Jul 2007 18:24:00 GMT | (1) camickra

 

> but keep getting a null pointer exception,

 

Where? We can't tell what the problem is based on a few lines of code.

 

Maybe its because you are trying to change the icon of the currently pressed button. If so then try wrapping your code in a SwingUtilities.invokeLater(...);

 

If you need further help then you need to create a [url http://homepage1.nifty.com/algafield/sscce.html]Short, Self Contained, Compilable and Executable, Example Program[/url] that demonstrates the incorrect behaviour, because I can't guess exactly what you are doing based on the information provided.

 

And don't forget to use the [url http://forum.java.sun.com/help.jspa?sec=formatting]Code Formatting Tags[/url] so the code retains its original formatting.

 

 

Sat, 14 Jul 2007 18:24:00 GMT | (2) fellovertodaya

 

import javax.swing.text.html.*;

import javax.swing.text.*;

import javax.swing.event.*;

import javax.swing.*;

import java.io.*;

import java.awt.*;

import java.awt.event.*;

import java.util.*;


public class button

{

public static void main(String[] args) 

{

JFrame f = new JFrame ();

final ImageIcon forwardButtonI = new ImageIcon("images/forwardButtonBlue.jpg");

final ImageIcon backButtonI = new ImageIcon("images/backButtonBlue.jpg");

JToolBar sliderBar = new JToolBar();

f.add(sliderBar);

//create forward and back buttons

final JButton forwardButton = new JButton (forwardButtonI );

final JButton backButton = new JButton (backButtonI);

sliderBar.add(backButton);

sliderBar.add(forwardButton);

forwardButton.addActionListener (new greenListener(forwardButton,backButton));

f.pack();

f.show(); 

}

}

class greenListener implements ActionListener {

private JButton backButton;

private JButton forwardButton;

public greenListener(JButton forwardButton, JButton backButton) {

}

public void actionPerformed(ActionEvent e) 

{ 

backButton.setIcon(new ImageIcon("images/backButtonGreen.jpg"));

}

}

 

 

Sat, 14 Jul 2007 18:24:00 GMT | (3) fellovertodaya

 

Thanks for your help, I have posted some example code above, hope you can spot where I have gone wrong

 

Sat, 14 Jul 2007 18:24:00 GMT | (4) michael_dunna

public greenListener(JButton forwardButton, JButton backButton) 
{
this.backButton = backButton;
this.forwardButton = forwardButton;

 

public greenListener(JButton forwardButton, JButton backButton) {

 

this.backButton = backButton;//<-

 

this.forwardButton = forwardButton;//<-

 

}

 

 

Sat, 14 Jul 2007 18:24:00 GMT | (5) fellovertodaya

 

oops silly mistakethanks

출처 : http://www.thatsjava.com/java-core-gui-apis/29631/