Develop Reference

Image location does not change in response to key events

package testapplication;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
public class TestApplication extends JFrame implements Runnable {
int sizex = 800;
int sizey = 650;
int x, y, xDirection, yDirection;
private Image dbImage;
private Graphics dbg;
Image character;
#Override
public void run(){
try{
while(true){
move();
Thread.sleep(5);
}
}
catch(Exception e){
System.out.println("ERROR!!!");
}
}
public void move(){
x += xDirection;
y += yDirection;
if(x <= 0)
x = 0;
if(x >= 778)
x = 778;
if(y <= 22)
y = 22;
if(y >= 628)
y = 628;
}
public void setXDirection(int xdir){
xDirection = xdir;
}
public void setYDirection(int ydir){
yDirection = ydir;
}
Font font = new Font("Arial", Font.BOLD, 30);
public class AL extends KeyAdapter {
#Override
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
//Key press inputs "WASD"
if(keyCode == KeyEvent.VK_W) {
setYDirection(-1);
}
if(keyCode == KeyEvent.VK_A) {
setXDirection(-1);
}
if(keyCode == KeyEvent.VK_S) {
setYDirection(+1);
}
if(keyCode == KeyEvent.VK_D) {
setXDirection(+1);
}
//end Key press inputs "WASD"
}
#Override
public void keyReleased(KeyEvent e) {
int keyCode = e.getKeyCode();
//Key release inputs "WASD"
if(keyCode == KeyEvent.VK_W) {
setYDirection(0);
}
if(keyCode == KeyEvent.VK_A) {
setXDirection(0);
}
if(keyCode == KeyEvent.VK_S) {
setYDirection(0);
}
if(keyCode == KeyEvent.VK_D) {
setXDirection(0);
}
//end Key release inputs "WASD"
}
}
public TestApplication() {
//Load images
ImageIcon i = new ImageIcon("C:/Users/Min/Documents/NetBeansProjects/TestApplication/src/testapplication/Untitled-1.png") {};
character = i.getImage();
//Game properties
addKeyListener(new AL());
setTitle("TestApplication");
setSize(sizex, sizey);
setResizable(false);
setVisible(true);
setBackground(Color.LIGHT_GRAY);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
x = 30;
y = 628;
}
#Override
public void paint(Graphics g) {
dbImage = createImage(getWidth(), getHeight());
dbg = dbImage.getGraphics();
paintComponent(dbg);
g.drawImage(dbImage, 0, 0, this);
}
public void paintComponent(Graphics g) {
g.setFont(font);
g.setColor(Color.RED);
g.drawString("Welcome to TESTTEST", 300,125);
g.setColor(Color.RED);
g.drawImage(character, x, y, this);
repaint();
}
public static void main(String[] args) {
TestApplication ta = new TestApplication();
//Threads
Thread t1 = new Thread();
t1.start();
}
}
In my Java code, there is supposed to be an image that moves using the WASD keys. The image shows, yet it will not move. What's wrong?
This is a simple Java code that is supposed to make an image roam around the window with WASD keys. I am not sure what I did wrong in the code, I've double checked and everything looked fine...

First of all, if you need to change the image location while the user presses one of the wsda keys then you need to add 1 and -1 to the current value of x and y ( image location). You just set 1 and -1 which will move the image just one pixel even if, for example, you press the d button multiple times over and over.
You need to change method setXDirection to this (I have added a plus before the equal sign to add xDir value to whatever xDirection is.)
public void setXDirection(int xDir)
{
xDirection += xDir
}
Make the same correction with yDirection (yDirection += yDir)
Second, you don't call your paint method. You have to call it each time your user presses a key (one of wasd ofcourse), so do it at the final line of your keyReleased method.
I hope these two correct your code but I think you need to recheck the code again with much care.
Good luck,
Iman

You forgot to add the Runnable instance to the Thread constructor.
Your main method should be:
public static void main(String[] args) {
TestApplication ta = new TestApplication();
//Threads
Thread t1 = new Thread(ta);
t1.start();
}

creating many objects with collision properties. JAVA

I have a simple program with three rectangles: one that can move with the push of the arrow keys, and two that are already moving back and forth on their own.
When the 'player' rectangle and top red collide, the player driven rectangle gets put back to (0,0). When I try to collide the player rectangle with the bottom red rectangle, it does not have those collision properties and I have no idea why.
What am I missing?
import java.awt.*;//needed for graphics
import javax.swing.*;//needed for JFrame window
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class javaapplication23 extends JFrame implements KeyListener, ActionListener {
public static int x = 0;
public static int y = 0;
public static int x2 = 100;
public static int y2 = 100;
public javaapplication23() {//constructor for JPanel
add(new JP());
}//close Jpanel Contructor
public static void main(String[] args) {
javaapplication23 w = new javaapplication23();
w.setTitle("MIKE IS AWESOME");
w.setSize(Toolkit.getDefaultToolkit().getScreenSize());
w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
w.setVisible(true);
w.addKeyListener(w);
}
public class JP extends JPanel {//start JPanel CLass
public JP() {
Container c = getContentPane();
c.setBackground(Color.white);//backgraund color can be changed
}
public void paint(Graphics g) {//opens paint method
super.paint(g);
player(g, x, y);
g.setColor(Color.RED);
enemylevel1(g, x2, y2);
Rectangle enemyblocks = new Rectangle(x2, y2, 25, 25);
Rectangle player = new Rectangle(x, y, 25, 25);
enemyblocks.contains(x2, y2);
player.contains(x, y);
if (player.getBounds().intersects(enemyblocks.getBounds())) {
x = 0;
y = 0;
}
pause(1);
repaint();
}//close paint method
}//close JPanel Class
public static void pause(int time) {
try //opens an exception handling statement
{
Thread.sleep(time);
} catch (InterruptedException e) {
} //captures the exception
}
public void actionPerformed(ActionEvent e) {
}
public void keyTyped(KeyEvent e) {
}
public void keyReleased(KeyEvent e) {
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == e.VK_RIGHT) {
x += 20;//global variable controlling right movement
repaint();
}
if (e.getKeyCode() == e.VK_LEFT) {
x -= 20;//global variable controlling left movement
repaint();
}
if (e.getKeyCode() == e.VK_UP) {
y -= 20;//global variable controlling up movement
repaint();
}
if (e.getKeyCode() == e.VK_DOWN) {
y += 20;//global variable controlling down movement
repaint();
}
}
public void player(Graphics g, int x, int y) {
g.fillRect(x, y, 30, 30);
}
public void enemylevel1(Graphics g, int x, int y) {
g.fillRect(x2, y2, 25, 25);
g.fillRect(x2, y2 + 100, 25, 25);
if (x2 < 200 && y2 == 100) {
x2 += 1;
}
if (x2 == 200 && y2 >= 100) {
y2 += 1;
}
if (x2 <= 200 && y2 >= 101) {
x2 -= 1;
}
if (x2 == 100 && y2 <= 101) {
y2 -= 1;
}
pause(10);
repaint();
}
}

Start by having a look at Working with Geometry, this will allow you to reduce much of the code complexity.
Basically, a enemy is just a Rectangle, Graphics2D can paint these without to much of an issue. What you need to do is create an instance which can also update it's position based on your needs
public class Enemy extends Rectangle {
private int xDelta;
public Enemy(int x, int y) {
super(x, y, 20, 20);
if (x == 0) {
xDelta = 1;
} else {
xDelta = -1;
}
}
public void update(Rectangle bounds) {
x += xDelta;
if (x < bounds.x) {
x = bounds.x;
xDelta *= -1;
} else if (x > bounds.x + bounds.width - width) {
x = bounds.x + bounds.width - width;
xDelta *= -1;
}
}
}
So, this creates a single unit of work, which is isolated from everything else and carries it's own logic with it. This makes updating it, painting and generally working with much simpler.
Next, you need to create a List of these
public class Bounce extends JPanel implements KeyListener, ActionListener {
private List<Enemy> enemies;
//...
public Bounce() {
enemies = new ArrayList<>(5);
int y = 100;
for (int index = 0; index < 5; index++) {
int x = (index % 2 == 0) ? 0 : 200;
Enemy enemy = new Enemy(x, y);
enemies.add(enemy);
y += 60;
}
This creates a List of Enemys which are distributed evenly within the container.
Now, we need to paint them....
#Override
protected void paintComponent(Graphics g) {//opens paint method
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g.create();
g2d.setColor(Color.RED);
for (Enemy enemy : enemies) {
g2d.fill(enemy);
}
}//close paint method
nb: General convention suggests that you should override paintComponent when you want to perform custom painting
But they don't move, that kind of sucks. So we need a way to, on a regular bases, update the position of the enemies...
First, we create a simple method which we can call to update the enemies, remember, they are capable of updating themselves, we just need to tell them when
public void updateState() {
Rectangle bounds = new Rectangle(20, 20, 200, 200);
for (Enemy enemy : enemies) {
enemy.update(bounds);
}
}
Remember, the Enemy is self contained, it knows how to update itself based on the constraints you have provided.
And now, we need to call this method on a regular bases...
javax.swing.Timer timer = new javax.swing.Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
updateState();
repaint();
}
});
timer.start();
Okay, this will schedule a callback every 40 milliseconds which will allow us to call the updateState method and repaint the component. This is neat because it won't block the Event Dispatching Thread (making our program look like it's hung) but which notifies us within the context of the EDT, making it safe to update the UI from within - WIN/WIN :)
Take a look at Concurrency in Swing and How to use Swing Timers for more details.
Okay, but that doesn't solve the collision...
The player is also a Rectangle, so why not use the same concept we have with the enemies...
public class Bounce extends JPanel implements KeyListener, ActionListener {
private List<Enemy> enemies;
private Rectangle player;
//...
public Bounce() {
player = new Rectangle(0, 0, 30, 30);
enemies = new ArrayList<>(5);
//...
}
#Override
protected void paintComponent(Graphics g) {//opens paint method
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
drawPlayer(g2d);
g2d.setColor(Color.RED);
for (Enemy enemy : enemies) {
g2d.fill(enemy);
if (player.intersects(enemy)) {
player.x = 0;
player.y = 0;
}
}
}//close paint method
public void drawPlayer(Graphics2D g) {
g.fill(player);
}
Which ends up with something like...
This allows you to add/remove enemies as you want and also change the way in which the enemies move, simply and easily
An my "awesome" test code...
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Bounce extends JPanel implements KeyListener, ActionListener {
private List<Enemy> enemies;
private Rectangle player;
public static void main(String[] args) {
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.add(new Bounce());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public Bounce() {
player = new Rectangle(0, 0, 30, 30);
enemies = new ArrayList<>(5);
int y = 100;
for (int index = 0; index < 5; index++) {
int x = (index % 2 == 0) ? 0 : 200;
Enemy enemy = new Enemy(x, y);
enemies.add(enemy);
y += 60;
}
setBackground(Color.white);//backgraund color can be changed
Timer timer = new Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
updateState();
repaint();
}
});
timer.start();
setFocusable(true);
requestFocusInWindow();
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
requestFocusInWindow();
}
});
addKeyListener(this);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(240, 400);
}
#Override
protected void paintComponent(Graphics g) {//opens paint method
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
drawPlayer(g2d);
g2d.setColor(Color.RED);
for (Enemy enemy : enemies) {
g2d.fill(enemy);
if (player.intersects(enemy)) {
player.x = 0;
player.y = 0;
}
}
}//close paint method
public void actionPerformed(ActionEvent e) {
}
public void keyTyped(KeyEvent e) {
}
public void keyReleased(KeyEvent e) {
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == e.VK_RIGHT) {
player.x += 20;//global variable controlling right movement
}
if (e.getKeyCode() == e.VK_LEFT) {
player.x -= 20;//global variable controlling left movement
}
if (e.getKeyCode() == e.VK_UP) {
player.y -= 20;//global variable controlling up movement
}
if (e.getKeyCode() == e.VK_DOWN) {
player.y += 20;//global variable controlling down movement
}
}
public void drawPlayer(Graphics2D g) {
g.fill(player);
}
public void updateState() {
Rectangle bounds = new Rectangle(20, 20, 200, 200);
for (Enemy enemy : enemies) {
enemy.update(bounds);
}
}
public class Enemy extends Rectangle {
private int xDelta;
public Enemy(int x, int y) {
super(x, y, 20, 20);
if (x == 0) {
xDelta = 1;
} else {
xDelta = -1;
}
}
public void update(Rectangle bounds) {
x += xDelta;
if (x < bounds.x) {
x = bounds.x;
xDelta *= -1;
} else if (x > bounds.x + bounds.width - width) {
x = bounds.x + bounds.width - width;
xDelta *= -1;
}
}
}
}

Add moving objects to JFrame

I'm creating a java game. In the game there are a hero and a bubble. The hero is supposed to move when I press the arrow keys and the bubble is supposed to have continuous diagonal movement. When I add the hero or the bubble directly into to the JFrame separately I get the desired behavior, but when I add them both I just get a very small square! I tried to add them to the same JPanel and after add that JPanel to the JFrame but it is not working. Probably I have to define some type of layout to the JPanels.
What am I doing wrong?
Code:
public class Pang {
public static void main(String[] args) {
JFrame f=new JFrame();
JPanel gamePanel=new JPanel();
gamePanel.setPreferredSize(new Dimension(800, 600));
DrawHero d=new DrawHero();
DrawBubble bubble=new DrawBubble();
gamePanel.add(d);
gamePanel.add(bubble);
f.add(gamePanel);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(800, 600);
}
}
public class DrawHero extends JPanel implements ActionListener, KeyListener {
Timer myTimer = new Timer(5, this);
int x = 0, y = 0, dx = 0, dy = 0, step = 10;
private transient Image imageHero = null;
public DrawHero() {
myTimer.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
imageHero = getHeroImage();
g2.drawImage(imageHero, x, y, 40, 40, null);
}
public Image getHeroImage() {
Image image = null;
image = getImage("hero.png");
return image;
}
public Image getImage(String path) {
Image tempImage = null;
try {
URL heroiURL = DrawHero.class.getResource(path);
tempImage = Toolkit.getDefaultToolkit().getImage(heroiURL);
} catch (Exception e) {
System.out.println("Error loading hero image! - "
+ e.getMessage());
}
return tempImage;
}
public void actionPerformed(ActionEvent e) {
repaint();
}
public void moveUp() {
y = y - step;
}
public void moveDown() {
y = y + step;
}
public void moveLeft() {
x = x - step;
}
public void moveRight() {
x = x + step;
}
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if (keyCode == KeyEvent.VK_UP) {
moveUp();
}
if (keyCode == KeyEvent.VK_DOWN) {
moveDown();
}
if (keyCode == KeyEvent.VK_LEFT) {
moveLeft();
}
if (keyCode == KeyEvent.VK_RIGHT) {
moveRight();
}
}
public void keyTyped(KeyEvent e) {
}
public void keyReleased(KeyEvent e) {
}
}
public class DrawBubble extends JPanel implements ActionListener, KeyListener {
Timer myTimer = new Timer(5, this);
int x = 100, y = 200, dx = 0, dy = 0, step = 10;
private transient Image imageHero = null;
public DrawBubble() {
myTimer.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.fill(new Ellipse2D.Double(x, y, 40, 40));
}
public void actionPerformed(ActionEvent e) {
x=x+dx;
y=y+dy;
repaint();
}
public void moveBubble() {
dy=2;
dx=2;
}
public void keyPressed(KeyEvent e) {
moveBubble();
}
public void keyTyped(KeyEvent e) {
}
public void keyReleased(KeyEvent e) {
}
}

I recommend that neither the DrawHero nor DrawBubble (which should be called Hero nor Bubble respectively) should extend any JComponent. Instead each should simply know how to draw itself to a Graphics object passed to it, when requested to do so.
Then a single GameField or PlayingArea class should keep references to all the Bubble objects and the Hero and draw call the draw(Graphics) method of those objects.
Using this approach it is not necessary to worry about layouts within the GameField component (they become irrelevant).
That is the basic strategy I pursue for rendering the stationary objects in this answer to [Collision detection with complex shapes.

When I add the hero or the bubble directly into to the JFrame separately I get the desired behavior, but when I add them both i just get a very small square!
The default layout manager for a JFrame is a BorderLayout. When you use add(component) without a constraint the component goes to the CENTER. Only one component can be added to the CENTER, so only the last one added is displayed.
I tried to add them to the same JPanel and after add that JPanel to the JFrame but it is not working.
The default layout manager for a JPanel is the FlowLayout which respects the preferred size of component. The problem is you don't override the getPreferredSize() method so the size is (0, 0) and there is nothing to paint.
Probably I have to define some type of layout to the JPanels.
Actually since you want random motion you need to use a null layout on the panel and then use the setSize() and setLocation() method of your components to position the components.
Then when you do this the custom painting should always be done at (0, 0) instead of (x, y) since the location will control where the component is painted on the panel.

Shapes not moving on drawing panel java

i am trying to make a simple java game with a bat(paddle) and ball. So far i have painted the 2 objects onto the panel, however i cant get them to move. i have added key events for the bat and a move() method for the ball. Below are all my classes.
Game class:
public class Game extends JFrame {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new Game();
}});
}
MyDrawingPanel myDrawingPanel = new MyDrawingPanel(this);
MyUIPanel myUIPanel = new MyUIPanel(this);
public Game()
{
setSize(1160,660); // you may change frame and panel sizes
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container cp = getContentPane();
cp.setLayout(new FlowLayout());
cp.add(myDrawingPanel);
cp.add(myUIPanel);
setVisible(true);
}
}
MyDrawingPanel class:
class MyDrawingPanel extends JPanel {
Game game;
Ball ball = new Ball(this);
Bat bat = new Bat(this);
public MyDrawingPanel(Game game)
{
this.game=game;
setPreferredSize(new Dimension(800,600));
setBackground(Color.RED);
requestFocus();
}
public void paint(Graphics g)
{
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
ball.paint(g2d);
Graphics2D gBat = (Graphics2D) g;
bat.paint(gBat);
}
}
Ball class:
public class Ball {
int x = 0;
int y = 0;
int xa = 1;
int ya = 1;
private MyDrawingPanel myDrawingPanel;
public Ball(MyDrawingPanel myDrawingPanel) {
this.myDrawingPanel = myDrawingPanel;
}
public void move() {
if (x + xa < 0)
xa = 1;
if (x + xa > myDrawingPanel.getWidth() - 30)
xa = -1;
if (y + ya < 0)
ya = 1;
if (y + ya > myDrawingPanel.getHeight() - 30)
ya = -1;
x = x + xa;
y = y + ya;
}
public void paint(Graphics2D g) {
g.fillOval(x, y, 30, 30);
}
}
Bat class:
public class Bat{
int x = 0;
int xa = 0;
private MyDrawingPanel myDrawingPanel;
public Bat(MyDrawingPanel myDrawingPanel)
{
this.myDrawingPanel = myDrawingPanel;
}
public void move(){
if(x + xa > 0 && x + xa <myDrawingPanel.getWidth()-60 )
x = x + xa;
}
public void paint(Graphics2D g)
{
g.setColor(Color.BLUE);
g.fillRoundRect(x, 500, 100, 20, 10, 10);
}
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode() == KeyEvent.VK_LEFT)
xa = -1;
if(e.getKeyCode() == KeyEvent.VK_RIGHT)
xa = 1;
}
public void keyReleased(KeyEvent e)
{
xa = 0;
}
}

Methods such as keyPressed and keyReleased don't do anything without a KeyListener implementation. So currently, your methods are useless. What you should do have the DrawingPanel class implement the KeyListener, like this
public class DrawingPanel extends JPanel implements KeyListener {
...
}
The methods, keyPressed and keyReleased should be in that class. You'll also want setter methods for what ever variables are updated in the Bat class, like x and xa, is those are the variables that determine the movement of the Bat.
So in the keyPressed, which should be in the DrawingPanel class, it could look something like this
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_LEFT) {
bat.setXa(bat.getXa() - 1);
repaint();
}
if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
bat.setXa(1);
repaint();
}
}
Notice how I call repaint(). That's what you need to do after you move something.
This should get you started in the right direction
EDIT Forget the majority of the above answer.
Instead of using a KeyListener though I would recommeng using key binding. You may face focus problems using KeyListener. I implemented the keybinding for the DrawingPanel and it works fine. It'll give you some ideas to work with.
class MyDrawingPanel extends JPanel {
Game game;
Ball ball = new Ball(this);
Bat bat = new Bat(this);
public MyDrawingPanel(Game game) {
this.game = game;
setPreferredSize(new Dimension(800, 600));
setBackground(Color.RED);
requestFocus();
Action rightAction = new AbstractAction() {
public void actionPerformed(ActionEvent e) {
bat.x += 10;
repaint();
}
};
Action leftAction = new AbstractAction() {
public void actionPerformed(ActionEvent e) {
bat.x -= 10;
repaint();
}
};
InputMap inputMap = getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW);
ActionMap actionMap = getActionMap();
inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "rightAction");
actionMap.put("rightAction", rightAction);
inputMap.put(KeyStroke.getKeyStroke("LEFT"), "leftAction");
actionMap.put("leftAction", leftAction);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
ball.paint(g2d);
Graphics2D gBat = (Graphics2D) g;
bat.paint(gBat);
}
}
See How to use key bindings

JFrame background color flashes but then reverts

Lately I've been attempting to replicate Space Invaders in java to help with learning about developing applications with java and the programming language in general. However I've run into a little problem with JFrame: the background color that I declared for the window doesn't stay, it just flashes and then reverts to the default. Here's my code:
import javax.imageio.ImageIO;`
import java.io.*;`
import javax.swing.*;`
import java.awt.*;`
import java.awt.image.*;`
import java.awt.image.ImageObserver;`
import java.awt.event.*;`
public class Invaders extends JPanel{
public static int x = 40;
public static int y = 345;
public static int h = 20;
public static int k = 180;
public static int move = 1;
static final Invaders m = new Invaders();
public static void main(String[] args){
final JFrame frame = new JFrame("Movement of 2d Shapes");
frame.setSize(404,390);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(m);
frame.setBackground(Color.BLACK);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
Action actionRight = new AbstractAction(){
public void actionPerformed(ActionEvent actionRightEvent){
if(x <= 350){
x += 10;
m.repaint();
};
}
};
Action actionLeft = new AbstractAction(){
public void actionPerformed(ActionEvent actionLeftEvent){
if(x >= 10){
x -= 10;
m.repaint();
};
}
};
KeyStroke right = KeyStroke.getKeyStroke("RIGHT");
KeyStroke left = KeyStroke.getKeyStroke("LEFT");
InputMap inputMap = m.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
inputMap.put(right, "RIGHT");
inputMap.put(left, "LEFT");
m.getActionMap().put("RIGHT", actionRight);
m.getActionMap().put("LEFT", actionLeft);
}
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
draw(g);
cpu_move(m);
}
public void cpu_move(Invaders m){
if(h == 0){
move = 0;
}else if(h == 375){
move = 1;
}
if(move == 0){
try {
Thread.sleep(60);
} catch (InterruptedException e) {
e.printStackTrace();
}
h += 5;
m.repaint();
}else if(move == 1){
try {
Thread.sleep(60);
} catch (InterruptedException e) {
e.printStackTrace();
}
h -= 5;
m.repaint();
};
}
public void draw(Graphics g){
try{
g.drawImage(ImageIO.read(getClass().getResource(
"images/Ship.jpg")), x, y, 35, 23, Color.BLACK, null);
g.drawImage(ImageIO.read(getClass().getResource(
"images/Alien.jpg")), h, k, 28, 20, Color.BLACK, null);
}catch(IOException k){
Component temporaryLostComponent = null;
JOptionPane.showMessageDialog(temporaryLostComponent,
"one or more image files missing or corrupt");
}
}
}
What's wrong with the declaration of the background color? there are no errors when compiling, but it still does this. What am I doing wrong?

Try next :
frame.getContentPane().add(m);
m.setBackground(Color.BLACK);
instead of frame.setBackground(Color.BLACK); because Invaders m fills all frame.
Your backgound will be black with image.

frame.getContentPane().add(m);
//frame.setBackground(Color.BLACK);
frame.getContentPane().setBackground( Color.BLACK );
Read the section from the Swing tutorial on Using Top Level Containters to understand the structure of a frame. The content pane is painted on top of the frame.