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KeyBinding multiple keys pressed not working

So I have a painted rectangle that I want to move with the arrow keys that includes diagonal movement, or rather allowance of multiple keys being pressed at the same time (In other words, movement that is similar to player movement in a 2D game). I have attempted to do this with a KeyListener, which was not working. So I decided to move to KeyBindings and I found an example from this website: https://coderanch.com/t/606742/java/key-bindings (Rob Camick's post)
I directly copied the code and it works as intended, except it is moving an icon and not a painted rectangle like I want to do. I have attempted to modify the code so that it would move a painted rectangle, but was only failing. Here is my latest attempt, which is also a minimal reproducible:
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
public class Test extends JPanel implements ActionListener
{
public JPanel component = this;
public int x = 100;
public int y = 100;
private Timer timer;
private int keysPressed;
private InputMap inputMap;
public void addAction(String name, int keyDeltaX, int keyDeltaY, int keyCode)
{
new NavigationAction(name, keyDeltaX, keyDeltaY, keyCode);
}
// Move the component to its new location
private void handleKeyEvent(boolean pressed, int deltaX, int deltaY)
{
keysPressed += pressed ? 1 : -1;
x += deltaX;
y += deltaY;
// Start the Timer when the first key is pressed
if (keysPressed == 1)
timer.start();
// Stop the Timer when all keys have been released
if (keysPressed == 0)
timer.stop();
}
// Invoked when the Timer fires
public void actionPerformed(ActionEvent e)
{
repaint();
}
class NavigationAction extends AbstractAction implements ActionListener
{
private int keyDeltaX;
private int keyDeltaY;
private KeyStroke pressedKeyStroke;
private boolean listeningForKeyPressed;
public NavigationAction(String name, int keyDeltaX, int keyDeltaY, int keyCode)
{
super(name);
this.keyDeltaX = keyDeltaX;
this.keyDeltaY = keyDeltaY;
pressedKeyStroke = KeyStroke.getKeyStroke(keyCode, 0, false);
KeyStroke releasedKeyStroke = KeyStroke.getKeyStroke(keyCode, 0, true);
inputMap.put(pressedKeyStroke, getValue(Action.NAME));
inputMap.put(releasedKeyStroke, getValue(Action.NAME));
component.getActionMap().put(getValue(Action.NAME), this);
listeningForKeyPressed = true;
}
public void actionPerformed(ActionEvent e)
{
// While the key is held down multiple keyPress events are generated,
// we only care about the first event generated
if (listeningForKeyPressed)
{
handleKeyEvent(true, keyDeltaX, keyDeltaY);
inputMap.remove(pressedKeyStroke);
listeningForKeyPressed = false;
}
else // listening for key released
{
handleKeyEvent(false, -keyDeltaX, -keyDeltaY);
inputMap.put(pressedKeyStroke, getValue(Action.NAME));
listeningForKeyPressed = true;
}
}
}
public void paintComponent(Graphics tool) {
super.paintComponent(tool);
System.out.println(x + ", " + y);
tool.drawRect(x, y, 50, 50);
}
public Test() {}
public static void main(String[] args)
{
new Test().create();
}
public void create() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
frame.setSize(600, 600);
frame.setLocationRelativeTo( null );
frame.getContentPane().add(component);
inputMap = component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
timer = new Timer(24, this);
timer.setInitialDelay( 0 );
addAction("Left", -3, 0, KeyEvent.VK_LEFT);
addAction("Right", 3, 0, KeyEvent.VK_RIGHT);
addAction("Up", 0, -3, KeyEvent.VK_UP);
addAction("Down", 0, 3, KeyEvent.VK_DOWN);
frame.setVisible(true);
}
}

Okay, so one of the issues I have with the code you've presented is the fact that you're leak responsibility. It's not the responsibility of the NavigationAction to register key bindings or modify the state the of UI. It should only be responsible for generating a notification that the state has changed back to a responsible handler.
This could be achieved through the use of some kind of model, which maintains the some kind of state, which is updated by the NavigationAction and read by the UI or, as I've chosen to do, via a delegation callback.
Another issue is, what happens when the user releases the key? Another issue is, how do you deal with the delay in repeated key press (ie when you hold the key down, there is a small delay between the first key event and the repeating key events)?
We can deal with these things through a simple change in mind set. Instead of using the NavigationAction to determine "what" should happen, it should be used to tell our UI "when" something has happened. In this a directional key has been pressed or released.
Instead of reacting to key stroke directly, we either "add" or "remove" the direction from a state model and allow the Swing Timer to update the state of the UI accordingly, this will generally be faster and smoother.
It also has the side effect of decoupling logic, as you no longer need to care about "how" the state was changed, only that it was and you can then decide how you want to react to it.
This approach is generally commonly used (in some form or another) in gaming engines.
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.util.HashSet;
import java.util.Set;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public interface KeyActionHandler {
public void keyActionPerformed(Direction direction, boolean pressed);
}
public enum Direction {
LEFT, RIGHT, DOWN, UP;
}
class NavigationAction extends AbstractAction implements ActionListener {
private KeyActionHandler keyActionHandler;
private Direction direction;
private Boolean pressed;
public NavigationAction(Direction direction, boolean pressed, KeyActionHandler keyActionHandler) {
this.direction = direction;
this.pressed = pressed;
this.keyActionHandler = keyActionHandler;
}
public void actionPerformed(ActionEvent e) {
keyActionHandler.keyActionPerformed(direction, pressed);
}
}
public class TestPane extends JPanel implements ActionListener, KeyActionHandler {
private int xDelta = 0;
private int yDelta = 0;
public int x = 100;
public int y = 100;
private Timer timer;
public TestPane() {
timer = new Timer(24, this);
InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap actionMap = getActionMap();
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "Pressed-Left");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "Pressed-Right");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false), "Pressed-Up");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, false), "Pressed-Down");
actionMap.put("Pressed-Left", new NavigationAction(Direction.LEFT, true, this));
actionMap.put("Pressed-Right", new NavigationAction(Direction.RIGHT, true, this));
actionMap.put("Pressed-Up", new NavigationAction(Direction.UP, true, this));
actionMap.put("Pressed-Down", new NavigationAction(Direction.DOWN, true, this));
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "Released-Left");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "Released-Right");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "Released-Up");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "Released-Down");
actionMap.put("Released-Left", new NavigationAction(Direction.LEFT, false, this));
actionMap.put("Released-Right", new NavigationAction(Direction.RIGHT, false, this));
actionMap.put("Released-Up", new NavigationAction(Direction.UP, false, this));
actionMap.put("Released-Down", new NavigationAction(Direction.DOWN, false, this));
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
#Override
public void addNotify() {
super.addNotify();
timer.start();
}
#Override
public void removeNotify() {
super.removeNotify();
timer.stop();
}
private Set<Direction> directions = new HashSet<>();
// Invoked when the Timer fires
#Override
public void actionPerformed(ActionEvent e) {
if (directions.contains(Direction.LEFT)) {
x -= 3;
} else if (directions.contains(Direction.RIGHT)) {
x += 3;
}
if (directions.contains(Direction.UP)) {
y -= 3;
} else if (directions.contains(Direction.DOWN)) {
y += 3;
}
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawRect(x, y, 50, 50);
}
#Override
public void keyActionPerformed(Direction direction, boolean pressed) {
if (pressed) {
directions.add(direction);
} else {
directions.remove(direction);
}
}
}
}
This is just one more approach to solve the same problem ;)
However, I am encountering a problem: it seems that removeNotify() is never called. I wanted to verify this and copied this post and pasted it into a new java file. I then added print statements in the add and remove notify methods, and only the print statement in the addNotify() method was printed. Also, if you add a print statement in the actionPerformed method, it prints repeatedly never ending
removeNotify is only called when the component, or a parent container, is removed.
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setLayout(new GridBagLayout());
JButton btn = new JButton("Remove");
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent evt) {
Container parent = getParent();
parent.remove(TestPane.this);
parent.revalidate();
parent.repaint();
}
});
add(btn);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
public void addNotify() {
super.addNotify();
System.out.println("Add");
}
#Override
public void removeNotify() {
super.removeNotify();
System.out.println("Remove");
}
}
}
I verified that removeNotify will be called through the hierarchy when a parent container is removed.

KeyListener method keyPressed not working

I am trying to make a little game using java swing and have gotten pretty far but now my KeyListener is not using the method keyPressed.
Here is some of my code
public class Screen extends JPanel implements Runnable{
private static final int WIDTH = 300, HEIGHT = 300, RIGHT = 0, LEFT = 1, UP = 2, DOWN = 3, STILL = 4;
private Thread thread;
private boolean running = false;
private int direction = DOWN;
public Screen() {
setFocusable(true);
addKeyListener(new Key());
setPreferredSize(new Dimension(WIDTH, HEIGHT));
start();
}
public void tick(){
System.out.println(direction)
}
public void start() {
running = true;
thread = new Thread(this, "Game Loop");
thread.start();
}
public void run() {
while (running) {
tick();
repaint();
}
}
private class Key implements KeyListener{
#Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
#Override
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
if (key == KeyEvent.VK_D) {
direction = RIGHT;
}
if (key == KeyEvent.VK_A) {
direction = LEFT;
}
if (key == KeyEvent.VK_W) {
direction = UP;
}
if (key == KeyEvent.VK_S) {
direction = DOWN;
}
}
#Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
}
}
I am looking at the console and expecting the output to change from 3 (which is DOWN) whatever button I press but it never does. After some time I realized that something was wrong with the keyPressed method, I just don't know what.

You don't need a separate "Game Loop" thread. Swing is event driven. Your key listener code will be called when the user presses a key on the computer keyboard.
As MadProgrammer mentioned in his comment to your question
modifying he state of the UI from outside the context of the EDT may cause painting issues
In other words, Swing is single threaded and that thread is referred to as the Event Dispatch Thread (EDT) and all your code that changes the GUI should be executed on the EDT only.
The below code is a stand-alone, Swing application that displays a focussable JPanel. When you press one of the relevant keyboard "direction" keys, i.e. A or D or S or W, the console displays the direction. Pressing any other key causes the direction STILL to be written to the console. Note that I used a enum for the various directions, rather than integer constants.
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
public class Screen01 extends JPanel implements Runnable {
public enum Directions {RIGHT, LEFT, UP, DOWN, STILL};
private static final int WIDTH = 300, HEIGHT = 300;
private Directions direction;
public Screen01() {
setPreferredSize(new Dimension(WIDTH, HEIGHT));
setFocusable(true);
addKeyListener(new Key());
}
public void run() {
createAndDisplayGui();
}
private void createAndDisplayGui() {
JFrame frame = new JFrame("Screen");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.add(this, BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private class Key implements KeyListener {
#Override
public void keyTyped(KeyEvent e) {
// Do nothing.
}
#Override
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
switch (key) {
case KeyEvent.VK_D:
direction = Directions.RIGHT;
break;
case KeyEvent.VK_A:
direction = Directions.LEFT;
break;
case KeyEvent.VK_W:
direction = Directions.UP;
break;
case KeyEvent.VK_S:
direction = Directions.DOWN;
break;
default:
direction = Directions.STILL;
}
System.out.println("Direction = " + direction);
}
#Override
public void keyReleased(KeyEvent e) {
// Do nothing.
}
}
public static void main(String[] args) {
EventQueue.invokeLater(new Screen01());
}
}

Make use of the key bindings API, it will solve this, and all other, KeyListener related issues without a lot of hacking and head scratching over why it "sometimes" works
Swing is single threaded. This means you should be careful about updating the state of the UI (directly or indirectly) from outside of the context of the Event Dispatching Thread, this also includes any state the UI might be dependent on.
Have a look at Concurrency in Swing for more details.
Without more details, one of the simplest solutions would be to use a Swing Timer to act as the primary "tick" action. Each time it "ticks" you'd inspect the state of the input and update the state of the model and trigger a repaint to update the UI
For example...
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.util.HashSet;
import java.util.Set;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public static class TestPane extends JPanel {
enum Input {
UP, DOWN, LEFT, RIGHT
}
private Set<Input> input = new HashSet<>();
public TestPane() {
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "Left.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "Left.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, false), "Right.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "Right.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false), "Up.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true), "Up.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, false), "Down.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, true), "Down.released");
am.put("Left.pressed", new InputAction(Input.LEFT, input, false));
am.put("Left.released", new InputAction(Input.LEFT, input, true));
am.put("Right.pressed", new InputAction(Input.RIGHT, input, false));
am.put("Right.released", new InputAction(Input.RIGHT, input, true));
am.put("Down.pressed", new InputAction(Input.DOWN, input, false));
am.put("Down.released", new InputAction(Input.DOWN, input, true));
am.put("Up.pressed", new InputAction(Input.UP, input, false));
am.put("Up.released", new InputAction(Input.UP, input, true));
input.add(Input.UP);
input.add(Input.DOWN);
input.add(Input.LEFT);
input.add(Input.RIGHT);
Timer timer = new Timer(5, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// Check what's currently been pressed
// and update the state accordingly...
if (input.contains(Input.UP)) {
//..
}
if (input.contains(Input.DOWN)) {
//..
}
if (input.contains(Input.LEFT)) {
//..
}
if (input.contains(Input.RIGHT)) {
//..
}
repaint();
}
});
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
int midX = getWidth() / 2;
int midY = getHeight() / 2;
FontMetrics fm = g2d.getFontMetrics();
int spaceWidth = fm.stringWidth("M");
int spaceHeight = fm.getHeight();
if (input.contains(Input.UP)) {
String text = "UP";
g2d.drawString(text,
midX - (fm.stringWidth(text)) / 2,
(midY - (spaceHeight * 2) + fm.getAscent()));
}
if (input.contains(Input.DOWN)) {
String text = "DOWN";
g2d.drawString(text,
midX - (fm.stringWidth(text)) / 2,
(midY + spaceHeight + fm.getAscent()));
}
if (input.contains(Input.LEFT)) {
String text = "LEFT";
g2d.drawString(text,
(midX - spaceWidth - fm.stringWidth(text)),
(midY + (fm.getAscent() / 2)));
}
if (input.contains(Input.RIGHT)) {
String text = "RIGHT";
g2d.drawString(text,
(midX + spaceWidth),
(midY + (fm.getAscent() / 2)));
}
g2d.dispose();
}
public class InputAction extends AbstractAction {
private Input input;
private Set<Input> inputSet;
private boolean onRelease;
public InputAction(Input input, Set<Input> inputSet, boolean onRelease) {
this.input = input;
this.inputSet = inputSet;
this.onRelease = onRelease;
}
#Override
public void actionPerformed(ActionEvent e) {
if (onRelease) {
inputSet.remove(input);
} else {
inputSet.add(input);
}
}
}
}
}
This is a basic example and prints the state of the key inputs directly within the paintComponent method. A more realistic implementation would use the Timer's ActionListener to inspect the input state and make changes to the desired model accordingly, which is hinted at in the example.
If you require more direct control, then you need to avoid the Swing painting system and take control yourself. For this, you'd need to use a BufferStrategy. This is a more complicated solution, but it is also more powerful, as you gain complete control over when the UI is updated

Smooth transition between moving left and right [duplicate]

I am trying to get a circle to move through the input of a keyboard. I am not able to move the object at all. Can someone help me figure out what is wrong? Here is my code:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JPanel;
public class AlienInvader extends JPanel implements KeyListener{
Constants constant = new Constants();
public void update() {
constant.x += constant.xvel;
addKeyListener(this);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.MAGENTA);
g.fillOval(constant.x, constant.y, 30, 30);
repaint();
}
#Override
public void keyPressed(KeyEvent e) {
System.out.println(constant.x);
switch(e.getKeyCode()) {
case KeyEvent.VK_LEFT:
constant.xvel = -1;
break;
case KeyEvent.VK_RIGHT:
constant.xvel = 1;
break;
}
}
#Override
public void keyReleased(KeyEvent e) {
switch(e.getKeyCode()) {
case KeyEvent.VK_LEFT:
constant.xvel = -1;
break;
case KeyEvent.VK_RIGHT:
constant.xvel = 1;
break;
}
}
#Override
public void keyTyped(KeyEvent arg0) {
// TODO Auto-generated method stub
}
}
I am not sure what I am doing wrong. I thought it was because I wasn't calling the update method, but when I added a if statement in paintComponent (so it only calls itself once) and tried it, I had no luck.

To start with, don't call repaint within any paintXxx method. Paint methods are typically called in response to a call to repaint, therefore you are creating a nasty, never ending, ever consuming loop of resource hell.
Secondly, KeyListeners only respond to key events when 1- The component the are registered to are focusable 2- When the component they are registered to have focus.
They are a poor choice in this case. Use Key bindings instead
Thirdly, you are not providing a preferredSize hint for layout managers to use. This may or may not be a bad thing in your case, but it's possible that you component will be laid out with a size of 0x0
Example
Something like....
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class MoveCircle {
public static void main(String[] args) {
new MoveCircle();
}
public MoveCircle() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private int xDelta = 0;
private int keyPressCount = 0;
private Timer repaintTimer;
private int xPos = 0;
private int radius = 10;
public TestPane() {
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "pressed.left");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "pressed.right");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "released.left");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "released.right");
am.put("pressed.left", new MoveAction(-2, true));
am.put("pressed.right", new MoveAction(2, true));
am.put("released.left", new MoveAction(0, false));
am.put("released.right", new MoveAction(0, false));
repaintTimer = new Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
xPos += xDelta;
if (xPos < 0) {
xPos = 0;
} else if (xPos + radius > getWidth()) {
xPos = getWidth() - radius;
}
repaint();
}
});
repaintTimer.setInitialDelay(0);
repaintTimer.setRepeats(true);
repaintTimer.setCoalesce(true);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.RED);
g2d.drawOval(xPos, 0, radius, radius);
g2d.dispose();
}
public class MoveAction extends AbstractAction {
private int direction;
private boolean keyDown;
public MoveAction(int direction, boolean down) {
this.direction = direction;
keyDown = down;
}
#Override
public void actionPerformed(ActionEvent e) {
xDelta = direction;
if (keyDown) {
if (!repaintTimer.isRunning()) {
repaintTimer.start();
}
} else {
repaintTimer.stop();
}
}
}
}
}
For example...

Java not detecting Keyboard Input (letters)

I'm making a 2d game engine and trying to improve the input system. When I try to use the WASD keys, the KeyListener sometimes won't detect the key being pressed but it still detects it being released. I tried using KeyBindings instead but I get the same problem. Anyone know what's going on?
(maybe it has something to do with my IDE(netbeans), mac, or java?)
edit: here's someone else's code that has the same problem
import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private Surface surface;
public TestPane() {
setLayout(new BorderLayout());
surface = new Surface();
InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap actionMap = getActionMap();
System.out.println("yo");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "Pressed.left");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "Release.left");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, false), "Pressed.right");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "Release.right");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false), "Pressed.up");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true), "Release.up");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, false), "Pressed.down");
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, true), "Release.down");
actionMap.put("Pressed.left", surface.getLeftPressAction());
actionMap.put("Release.left", surface.getLeftReleaseAction());
actionMap.put("Pressed.right", surface.getRightPressAction());
actionMap.put("Release.right", surface.getRightReleaseAction());
actionMap.put("Pressed.up", surface.getUpPressAction());
actionMap.put("Release.up", surface.getUpReleaseAction());
actionMap.put("Pressed.down", surface.getDownPressAction());
actionMap.put("Release.down", surface.getDownReleaseAction());
add(surface);
}
}
public class Surface extends Canvas {
private String displayText = "...";
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g.create();
FontMetrics fm = g2d.getFontMetrics();
int x = (getWidth() - fm.stringWidth(displayText)) / 2;
int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
g2d.drawString(displayText, x, y);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
public Action getLeftPressAction() {
return new TextAction("Left");
}
public Action getLeftReleaseAction() {
return new ClearAction();
}
public Action getRightPressAction() {
return new TextAction("Right");
}
public Action getRightReleaseAction() {
return new ClearAction();
}
public Action getUpPressAction() {
return new TextAction("Up");
}
public Action getUpReleaseAction() {
return new ClearAction();
}
public Action getDownPressAction() {
return new TextAction("Down");
}
public Action getDownReleaseAction() {
return new ClearAction();
}
public class TextAction extends AbstractAction {
private String text;
public TextAction(String text) {
this.text = text;
}
#Override
public void actionPerformed(ActionEvent e) {
displayText = text;
repaint();
}
}
public class ClearAction extends AbstractAction {
#Override
public void actionPerformed(ActionEvent e) {
displayText = "...";
repaint();
}
}
}
}

I just tried using the jar file in a windows 10 and it worked perfectly... It may have something to do with my operating system or my version of java.

KeyListener works, but doesn't

Im newish to keylistener, but recently I made a little program which will be below, which uses keylistener to make the A,W,S,D keys move a square. Well I used dropbox to get the program on this laptop, and now it doesn't work. It seems weird to me that it works on a keyboard, but not on a laptop keyboard. Any ideas why? Here is the code, well a portion:
public class Game extends JApplet implements KeyListener
{
public boolean isMoving = false;
int test = 0;
Rect r = new Rect();
public void keyPressed(KeyEvent e){}
public void keyReleased(KeyEvent e){} // ignore
public void keyTyped(KeyEvent e)
{
char keyChar = e.getKeyChar();
if (keyChar == KeyEvent.VK_S)
{
r.yVelocity -= 1;
}
if (keyChar == KeyEvent.VK_W)
{
r.yVelocity+=1;
}
if (keyChar == KeyEvent.VK_A)
{
r.xVelocity -=1;
}
if (keyChar == KeyEvent.VK_D)
{
r.xVelocity +=1;
}
}

KeyListener has focus issues. That is, it will only respond to key events when is focusable AND has focus.
The simply solution would be to make the component which the KeyListener is registered to focusable and use requestFocusInWindow, but this makes no gurentees that the component will recieve key board focus.
A better solution would be to use the Key Bindings API which allows you to configure the focus level required for key events to be raised...
Updated with a key bindings example/test
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.geom.AffineTransform;
import java.awt.geom.Path2D;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class TestKeyBindings {
public static void main(String[] args) {
new TestKeyBindings();
}
public TestKeyBindings() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new KeyPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class KeyPane extends JPanel {
private Triangle up;
private Triangle down;
private Triangle left;
private Triangle right;
private Set<String> activeKeys;
public KeyPane() {
activeKeys = new HashSet<>(4);
up = new Triangle(20);
down = new Triangle(20);
left = new Triangle(20);
right = new Triangle(20);
AffineTransform at = AffineTransform.getRotateInstance(Math.toRadians(-90), 10, 10);
left.transform(at);
at = AffineTransform.getRotateInstance(Math.toRadians(180), 10, 10);
down.transform(at);
at = AffineTransform.getRotateInstance(Math.toRadians(-270), 10, 10);
right.transform(at);
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false), "upPressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, false), "downPressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "leftPressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "rightPressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "upReleased");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "downReleased");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "leftReleased");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "rightReleased");
ActionMap am = getActionMap();
am.put("upPressed", new DirectionAction("up", true));
am.put("downPressed", new DirectionAction("down", true));
am.put("leftPressed", new DirectionAction("left", true));
am.put("rightPressed", new DirectionAction("right", true));
am.put("upReleased", new DirectionAction("up", false));
am.put("downReleased", new DirectionAction("down", false));
am.put("leftReleased", new DirectionAction("left", false));
am.put("rightReleased", new DirectionAction("right", false));
}
public void addKey(String name) {
activeKeys.add(name);
repaint();
}
public void removeKey(String name) {
activeKeys.remove(name);
repaint();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
int x = (getWidth() - (up.getBounds().width * 3)) / 2;
int y = (getHeight() - 10) / 2;
AffineTransform at = AffineTransform.getTranslateInstance(x, y);
if (activeKeys.contains("left")) {
g2d.fill(left.createTransformedShape(at));
} else {
g2d.draw(left.createTransformedShape(at));
}
at = AffineTransform.getTranslateInstance(x + 40, y);
if (activeKeys.contains("right")) {
g2d.fill(right.createTransformedShape(at));
} else {
g2d.draw(right.createTransformedShape(at));
}
at = AffineTransform.getTranslateInstance(x + 20, y - 20);
if (activeKeys.contains("up")) {
g2d.fill(up.createTransformedShape(at));
} else {
g2d.draw(up.createTransformedShape(at));
}
at = AffineTransform.getTranslateInstance(x + 20, y + 20);
if (activeKeys.contains("down")) {
g2d.fill(down.createTransformedShape(at));
} else {
g2d.draw(down.createTransformedShape(at));
}
g2d.dispose();
}
public class DirectionAction extends AbstractAction {
private String name;
private boolean pressed;
public DirectionAction(String name, boolean pressed) {
this.name = name;
this.pressed = pressed;
}
#Override
public void actionPerformed(ActionEvent e) {
if (pressed) {
addKey(name);
} else {
removeKey(name);
}
}
}
}
public class Triangle extends Path2D.Double {
public Triangle(int size) {
moveTo(size / 2, 0);
lineTo(size, size);
lineTo(0, size);
closePath();
}
}
}