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KeyListener not responding to key inputs [duplicate]

This question already has an answer here:
Pong Paddle bottom doesn't move up when UP key is pressed
(1 answer)
Closed 7 years ago.
So I have seen a couple of these questions asked. They all say that you should not be using a Keylistener but instead a KeyBinding thing. But when I go to use the Keybinding it does not work. I understand I probably should be using the KeyBinding thing but is there a way that I can fix my code so that the KeyListener works. Thank you.
Game Class:
public class Game extends JFrame implements KeyListener{
public static int ppx,ppy;
public static void main(String[] args) {
JFrame frame = new JFrame("Game");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500,600);
frame.add(new THIng());
frame.setVisible(true);
}
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyPressed(KeyEvent e) {
int keycode = e.getKeyCode();
if(keycode == KeyEvent.VK_D){
System.out.println("Debug");
}
}
#Override
public void keyReleased(KeyEvent e) {
}
}
THIng Class:
public class THIng extends JPanel{
public static int px,py,pwid,phei;
public void main(String[]args){
Timer timer;
timer = new Timer(60,
new ActionListener(){
public void actionPerformed(ActionEvent evt){
p();
}
}
);
}
public THIng(){
px = Game.ppx;py = Game.ppy;pwid = 50;phei = pwid;
}
#Override
public Dimension getPreferredSize(){
return new Dimension(500,600);
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics p = (Graphics)g;
p.drawRect(px,py,pwid,phei);
}
public void p(){
repaint();
}
}

you don't have to make a constructor, just add frame.addKeyListener(this); where you have set other properties of the JFrame.

as MadProgrammer has pointed out the right thing to do is use the Key Bindings API which you can see step by step Key Bindings API
add a constructor that adds a key listener and in your main make it class Game instead of JFrame
public class Game extends JFrame implements KeyListener{
public static int ppx,ppy;
public Game(String string) {
addKeyListener(this);
// TODO Auto-generated constructor stub
}
public static void main(String[] args) {
Game frame = new Game("Game");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500,600);
frame.add(new THIng());
frame.setVisible(true);
}
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyPressed(KeyEvent e) {
int keycode = e.getKeyCode();
if(keycode == KeyEvent.VK_D){
System.out.println("Debug");
}
}
#Override
public void keyReleased(KeyEvent arg0) {
// TODO Auto-generated method stub
}
}

Two JButtons using the same actionListener to Start/Stop Timer

I'm fairly new to Java and could do with some help. I trying to make a Timer countdown from a set time to 0. I have this functionality working fine, but I want to add functionality to allow me to stop the Timer as it's counting down.
Here is my code (I'm trying to achieve this using MVC)
This is the control part:
import java.awt.event.*;
import javax.swing.*;
public class StartButton extends JButton implements ActionListener
{
private TimerModel model;
private Timer timer;
private boolean isStarted;
public StartButton(String buttonText, TimerModel model)
{
super(buttonText);
addActionListener(this);
this.model = model;
isStarted = false;
}
public void actionPerformed(ActionEvent evt)
{
if(!isStarted)
{
timer = new Timer(1000, this);
timer.start();
isStarted = true;
}
model.timerCountdown();
}
public void stopTimer()
{
timer.stop();
}
}
I have looked at some other similar issues online and I tried this within the constructor (Note: I didn't use implements ActionListener, and removed the actionPerformed method I had above):
if(buttonText.equals("Start"))
{
addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
if(!isStarted)
{
timer = new Timer(1000, this);
timer.start();
isStarted = true;
}
model.timerCountdown();
}
});
}
if(buttonText.equals("Stop"))
{
addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
timer.stop();
}
});
}
Now this part handles the counting down ok, but when I click the stop button it shows an exception(See stack trace here), and it continues to count down.
I have limited knowledge, but I guess it's something to do with the way I'm trying to stop the Timer.
I would appreciate it if someone could point me in the right direction, or at least explain to me why this happens.

Again, if you're not changing the basic behavior of the JButton itself, such as how it is drawn, but instead are only changing the button's title and behavior when pressed, then don't extend JButton. Instead give each button its own Action, an object from a class that extends from AbstractAction. Consider these guys as similar to ActionListeners on steroids. They have the same abilities as ActionListeners and then some since they can easily change the button's title, whether it is enabled or not, its mnemonic, icon,...
For example:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.event.*;
import javax.swing.*;
#SuppressWarnings("serial")
public class MyTimerGui {
private static final String TITLE = "Flashing Label";
private static final int TIMER_DELAY = 200;
private static final int GAP = 3;
private static final float LABEL_POINTS = 32F;
private JPanel mainPanel = new JPanel();
private JLabel flashyLabel = new JLabel(TITLE, SwingConstants.CENTER);
private Timer timer = new Timer(TIMER_DELAY, new TimerListener());
public MyTimerGui() {
Font font = flashyLabel.getFont();
font = font.deriveFont(LABEL_POINTS);
flashyLabel.setFont(font);
flashyLabel.setOpaque(true);
JPanel buttonPanel = new JPanel(new GridLayout(1, 0, GAP, 0));
buttonPanel.add(new JButton(new StartAction(this, "Start", KeyEvent.VK_S)));
buttonPanel.add(new JButton(new StopAction(this, "Stop", KeyEvent.VK_T)));
buttonPanel.add(new JButton(new ExitAction(this, "Exit", KeyEvent.VK_X)));
mainPanel.setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
mainPanel.setLayout(new BorderLayout());
mainPanel.add(flashyLabel, BorderLayout.CENTER);
mainPanel.add(buttonPanel, BorderLayout.PAGE_END);
}
public JComponent getMainComponent() {
return mainPanel;
}
public void start() {
timer.start();
}
public void stop() {
timer.stop();
flashyLabel.setForeground(null);
flashyLabel.setBackground(null);
}
public void exit() {
timer.stop();
Window win = SwingUtilities.getWindowAncestor(mainPanel);
win.dispose();
}
private class TimerListener implements ActionListener {
private final Color foreground1 = Color.green;
private final Color background1 = Color.red;
#Override
public void actionPerformed(ActionEvent aEvt) {
Color fg = flashyLabel.getForeground();
if (foreground1.equals(fg)) {
flashyLabel.setForeground(null);
flashyLabel.setBackground(null);
} else {
flashyLabel.setForeground(foreground1);
flashyLabel.setBackground(background1);
}
}
}
private class StartAction extends AbstractAction {
private MyTimerGui myTimerGui;
public StartAction(MyTimerGui myTimerGui, String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
this.myTimerGui = myTimerGui;
}
#Override
public void actionPerformed(ActionEvent e) {
myTimerGui.start();
}
}
private class StopAction extends AbstractAction {
private MyTimerGui myTimerGui;
public StopAction(MyTimerGui myTimerGui, String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
this.myTimerGui = myTimerGui;
}
#Override
public void actionPerformed(ActionEvent e) {
myTimerGui.stop();
}
}
private class ExitAction extends AbstractAction {
private MyTimerGui myTimerGui;
public ExitAction(MyTimerGui myTimerGui, String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
this.myTimerGui = myTimerGui;
}
#Override
public void actionPerformed(ActionEvent e) {
myTimerGui.exit();
}
}
private static void createAndShowGui() {
MyTimerGui myTimerGui = new MyTimerGui();
JFrame frame = new JFrame("MyTimer");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(myTimerGui.getMainComponent());
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

I agree with the comments that say you shouldn't be extending a JButton. Maybe the logic should be carried out in the main class of your application, the same class that class that deals with the creation and storage of the components.
But I digress. To answer your question, I think there are really two ways to approach this. Either (A) have the actionListener stored within your class as you did in your code or (B) write an actionListener outside of the object itself.
Was the constructor you tried to implement this in the main class constructor?
I think you need something like the following (this, again, is in the main class):
StartButton start = new JButton("Start");
StopButton stop = new JButton("Stop");
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// called when the button is pressed
buttonPressed();
}
});
stop.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// called when the button is pressed
buttonPressed();
}
});
Then you would write this method in the same class:
private void buttonPressed() {
System.out.println("Button pressed!");
}
I just whipped up a quick test of this, so I can confirm that this method works.
PS: I would also suggest having the button contain a boolean state instead of checking for the text of the button, if you do intend to keep using the StartButton and associated classes.

Cannot make a keylistener work

I have public class MainFrame extends JFrame implements ActionListener {
and then later on:
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == e.VK_LEFT) {
int x = ball.getX() + 1;
ball.setX(x);
}
}
however it does not seem to respond when I believe it should.
If I add keylistener instead of actionlister I cannot compile which I can't understand. I'm new to java however i'm used to C#

You need to implement java.awt.event.KeyListener not a ActionListener to listen for key events.
You need to register your listener on the element (frame) you want to listen on by invoking addKeyListener(...).
Example:
public class TestFrame extends JFrame implements KeyListener {
public static void main(String[] args) throws FileNotFoundException {
TestFrame testFrame = new TestFrame();
testFrame.setSize(100, 100);
testFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
testFrame.addKeyListener(testFrame);
testFrame.setVisible(true);
}
#Override
public void keyTyped(KeyEvent e) { }
#Override
public void keyPressed(KeyEvent e) {
System.out.println(e);
}
#Override
public void keyReleased(KeyEvent e) { }
}

No up state JButton

I'm trying to change to appearance of my JButton so that the button have no up state.
Currently i have something like this:
And i would like something like this:(comming from NetBeans)
In other words, I only want the image of the button to be visible when the button does not have any kind of focus. But when the user click or roll over it, it should act exactly the same as a regular button.
more examples:
no focus
roll over
click
I use a inner class for my button. It look like this:
private class CustumJButton extends JButton
{
public CustumJButton(Icon icon)
{
super(icon);
int size = 30;
setPreferredSize(new Dimension(size, size));
setFocusable(false);
}
}
Thanks ayoye.

You can achieve this using setBorderPainted() and setContentAreaFilled() methods. Here is the short Demo of what you are looking for. I hope it would give you rough figure to how to achieve your task.:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class CustomJButton extends JButton
{
public CustomJButton(String icon)
{
super(icon);
/*int size = 30;
setPreferredSize(new Dimension(size, size));*/
addFocusListener(new ButtonFocusAdapter());
addMouseListener(new ButtonMouseAdapter());
setContentAreaFilled(false);
setBorderPainted(false);
//setFocusable(false);//Don't use this method. This would avoid the focus event on JButton
}
private void decorateButton()
{
setContentAreaFilled(true);
setBorderPainted(true);
}
private void unDecorateButton()
{
setContentAreaFilled(false);
setBorderPainted(false);
}
private class ButtonFocusAdapter extends FocusAdapter
{
#Override
public void focusGained(FocusEvent evt)
{
decorateButton();
}
#Override
public void focusLost(FocusEvent evt)
{
unDecorateButton();
}
}
private class ButtonMouseAdapter extends MouseAdapter
{
#Override
public void mouseEntered(MouseEvent evt)
{
decorateButton();
}
#Override
public void mouseExited(MouseEvent evt)
{
unDecorateButton();
}
}
}
public class ButtonFrame extends JFrame
{
public void createAndShowGUI()
{
Container c = getContentPane();
c.setLayout(new FlowLayout());
for (int i = 0; i < 4 ; i++ )
{
CustomJButton cb = new CustomJButton("Button "+i);
c.add(cb);
}
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String st[])
{
SwingUtilities.invokeLater( new Runnable()
{
#Override
public void run()
{
ButtonFrame bf = new ButtonFrame();
bf.createAndShowGUI();
bf.setLocationRelativeTo(null);
}
});
}
}

I guess you need to use these two things to make it work, setBorderPainted(boolean) and setContentAreaFilled(boolean)
buttonObject.setBorderPainted(false);
buttonObject.setContentAreaFilled(false);
as cited in this example for changing appearance of JButton by #mKorbel
import java.awt.*;
import java.awt.event.*;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
public class ButtonDemo
{
private JButton demoButton;
private ImageIcon buttonImage;
private void displayGUI()
{
JFrame frame = new JFrame("Button Demo Example");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JPanel contentPane = new JPanel();
try
{
//buttonImage = new ImageIcon(ImageIO.read(
// getClass().getResource("/image/bulb.gif")));
buttonImage = new ImageIcon(ImageIO.read(
new URL("http://gagandeepbali.uk.to/"
+ "gaganisonline/swing/downloads/"
+ "images/bulb.gif")));
}
catch(Exception e)
{
e.printStackTrace();
}
demoButton = new JButton(buttonImage);
setExceptionalState(demoButton);
demoButton.addMouseListener(new MouseAdapter()
{
#Override
public void mouseEntered(MouseEvent me)
{
setNormalState(demoButton);
}
#Override
public void mouseExited(MouseEvent me)
{
setExceptionalState(demoButton);
}
});
contentPane.add(demoButton);
frame.setContentPane(contentPane);
frame.setSize(300, 100);
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private void setExceptionalState(JButton button)
{
button.setBorderPainted(false);
button.setContentAreaFilled(false);
}
private void setNormalState(JButton button)
{
button.setBorderPainted(true);
button.setContentAreaFilled(true);
}
public static void main(String[] args)
{
Runnable runnable = new Runnable()
{
#Override
public void run()
{
new ButtonDemo().displayGUI();
}
};
EventQueue.invokeLater(runnable);
}
}

You would set the default state for the button as:
button.setBorderPainted(false);
Then you would need to use a MouseListener:
on mouseEntered you would use
button.setBorderPainted(true);
and on mouse exited you would use
button.setBorderPainted(false);

You should check out the skinnable "Synth Look and Feel", but also be aware that Swing will be deprecated and replaced by JavaFX in the long run. If you are building a new application, you might want to consider using JavaFX which can be skinned with CSS to achieve the effect you are looking for.

Keylistener not working for JPanel

I am trying to do something when one of the arrow keys are pressed using the KeyListener in my JPanel class. Here is my code:
public class TestPanel extends JPanel implements KeyListener{
public TestPanel(){
this.addKeyListener(this);
this.setFocusable(true);
this.requestFocusInWindow();
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
System.out.println("Right");
}
if (e.getKeyCode() == KeyEvent.VK_LEFT) {
System.out.println("Left");
}
}
public void keyTyped(KeyEvent e) {}
public void keyReleased(KeyEvent e) {}
}
My main method adds a new instance of this panel to a frame and displays it. Do I need to add the keylistener to the JFrame? In my case, this would be difficult and inefficient, so I would like to make it work with this JPanel if possible. Anyone know what I am doing wrong?
EDIT: Key Bindings code that does not work either:
public class GamePanel extends JPanel implements ActionListener{
//Constructor
public GamePanel(){
setupKeyBinding();
this.setFocusable(true);
this.requestFocusInWindow();
}
private void setupKeyBinding() {
int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
InputMap inMap = getInputMap(condition);
ActionMap actMap = getActionMap();
inMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "Left");
actMap.put("Left", new leftAction());
}
private class leftAction extends AbstractAction {
public void actionPerformed(ActionEvent e) {
System.out.println("test");
}
}
public void actionPerformed(ActionEvent e) {
//some other game info
}
}
Can someone tell me why this doesnt work either? (my second action listener is for other stuff needed for my game)

If you search this problem, you'll see that it is asked and has been solved many times.
KeyListeners need to be on the focused component to work. One solution is to give your component the focus after first making it focusable.
Better by a long shot however is to use Key Bindings. Google the tutorial on this.
Please have a look at my answer to this question for more on this, including many of the gory details.

For reference, I've create an example using your approach; while it works, it also suggests a focus problem elsewhere in your code. Key Bindings avoid this, as shown here.
Addendum: Here's my working key binding.
private static class TestPanel extends JPanel {
private static final String LEFT = "Left";
private Action left = new AbstractAction(LEFT) {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println(LEFT);
}
};
private static final String RIGHT = "Right";
private Action right = new AbstractAction(RIGHT) {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println(RIGHT);
}
};
public TestPanel() {
this.getInputMap().put(
KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), LEFT);
this.getActionMap().put(LEFT, left);
this.getInputMap().put(
KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), RIGHT);
this.getActionMap().put(RIGHT, right);
}
}
Original SSCCE:
import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
/**
* #see https://stackoverflow.com/a/16531380/230513
*/
public class Test {
private void display() {
JFrame f = new JFrame("Test");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new TestPanel());
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
private static class TestPanel extends JPanel implements KeyListener {
public TestPanel() {
this.addKeyListener(this);
this.setFocusable(true);
this.requestFocusInWindow();
}
#Override
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
System.out.println("Right");
}
if (e.getKeyCode() == KeyEvent.VK_LEFT) {
System.out.println("Left");
}
}
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyReleased(KeyEvent e) {
}
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
new Test().display();
}
});
}
}

For receives key events on JPanel you must set focus:
setFocusable(true);
requestFocus();
the JPanel now has focus, so it receives key events

I had to do two things: I added comp.setFocusable(true); to the component comp that listens to key events, and I added comp.requestFocus(); to each action which caused comp to lose the focus.