Develop Reference

Java drawing moving rectangles in loop

I need to draw in AWT/Swing rectangles that are moving from frame to frame.
I have a Playground class
public Playground(int sizeX, int sizeY)
{
frame = new JFrame();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel = new JPanel();
panel.setSize(sizeX, sizeY);
panel.setDoubleBuffered(true);
panel.setVisible(true);
frame.add(panel);
frame.pack();
frame.setSize(sizeX, sizeY);
}
public void refresh()
{
panel.repaint();
}
public Graphics getGraphics()
{
return panel.getGraphics();
}
This is the class in which objects should be drawn:
public class Star {
private static int size = 10;
private int posX;
private int posY;
public Star(int posX, int posY)
{
this.posX = posX;
this.posY = posY;
}
public void paint(Graphics g)
{
g.fillRect(posX, posY, size, size);
}
public int getPosX() {
return posX;
}
public int getPosY() {
return posY;
}
}
This is the main method:
public static void main(String[] args) {
Playground playground = new Playground(400, 400);
Star star = new Star(100, 100);
Star star2 = new Star(125, 125);
while(1 == 1)
{
playground.refresh();
star.paint(playground.getGraphics());
star2.paint(playground.getGraphics());
}
}
The objects are drawn but are flickering, how can I stop it from flickering?
Edit: I solved the flickering for one element, by changing the refresh method to:
public void refresh()
{
panel.getGraphics().clearRect(0,0, panel.getWidth(), panel.getHeight());
}
Unfortunately only one Element is not flickering all others are still flickering.

The following is a one-file mcve that demonstrates moving (rotating for simplicity) a rectangle by custom painting.
One-file meaning that you can copy-paste the entire code into one file (AnimateRectangle.java) and execute it.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class AnimateRectangle {
private JFrame frame;
public AnimateRectangle(Model model){
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new MyJPanel(model);
panel.setDoubleBuffered(true);
frame.add(panel);
frame.pack();
frame.setVisible(true);
}
void refresh() {
frame.repaint();
}
public static void main(String[] args) throws InterruptedException {
Controller controller = new Controller(400, 400);
while (true) {
Thread.sleep(1000);
SwingUtilities.invokeLater(()->controller.animate());
}
}
}
//"wires" gui and model
class Controller{
private Model model;
private AnimateRectangle view;
Controller(int sizeX, int sizeY){
model = new Model(sizeX, sizeY);
view = new AnimateRectangle(model);
}
void animate() {
int newAngle = (model.getAngle() < 360 ) ? model.getAngle()+1 : 0 ;
model.setAngle(newAngle);
view.refresh();
}
}
//represents the inforamtion the GUI needs
class Model{
int sizeX, sizeY, angle = 0;
public Model(int sizeX, int sizeY) {
this.sizeX = sizeX;
this.sizeY = sizeY;
}
int getSizeX() { return sizeX; }
int getSizeY() {return sizeY;}
int getAngle() {return angle;}
//degrees
void setAngle(int angle) { this.angle = angle; }
}
//a JPanel with custom paint component
class MyJPanel extends JPanel {
private Model model;
public MyJPanel(Model model) {
this.model = model;
setPreferredSize(new Dimension(model.getSizeX(), model.getSizeY()));
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setColor(Color.RED);
int sizeX = model.getSizeX(), sizeY = model.getSizeY();
g2d.rotate(Math.toRadians(model.getAngle()), sizeX /2, sizeY/2);
g2d.fillRect(sizeX/4, sizeY/4, sizeX/2, sizeY/2);
}
}
A better option (see camickr comment) is to animate using swing Timer. To do so, remove animate() method, and replace it with :
void animateWithTimer(){
new Timer(1000,new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
int newAngle = (model.getAngle() < 360 ) ? model.getAngle()+1 : 0 ;
model.setAngle(newAngle);
view.refresh();
}
}).start();
}
and change main to use it :
public static void main(String[] args) throws InterruptedException {
Controller controller = new Controller(400, 400);
controller.animateWithTimer();
}

Placement of a JPanel within a JPanel

I'm trying to code a simple Pong and I have the background panel which contains a Bar panel. So of course I need to be able to place the bar on the size and move it vertically at request. Now I'm just trying to put it in a starting position. If I don't disable the layout the bar gets placed in the top center regardless of location setting, but if I disable the layout and set location it just doesn't show up. I'm not sure what I missing. Here is a code snippet if it can be relevant:
public PongPanel() {
setLayout(null);
setPreferredSize(SIZE);
setBackground(Color.BLACK);
player_one_bar = new Bar();
add(player_one_bar);
player_one_bar.setLocation(10, getSize().height/2-3);
}

If you set the layout manager as null you'll have to specify the exact coordinates of the panel, meaning something like -
setBounds(10, 10, 20, 100);
Will put the panel at location (10,10) with Width of 20 and Height of 100.

If by "bar" you mean Pong game paddle, then it shouldn't be a component at all but rather a logical entity that represents a position, which is visually represented by a sprite that gets drawn in the JPanel's paintComponent method.
For example:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class PongPaddle extends JPanel {
private static final int PREF_W = 800;
private static final int PREF_H = 500;
private static final int RECT_X = 20;
private static final int RECT_W = 10;
private static final int RECT_H = 60;
private static final int STARTING_Y = (PREF_H - RECT_H) / 2;
private static final int TIMER_DELAY = 15;
private static final int DELTA_PADDLE = 3;
private boolean paddle1GoingDown = true;
private boolean paddle2GoingDown = false;
private Rectangle paddle1 = new Rectangle(RECT_X, STARTING_Y, RECT_W, RECT_H);
private Rectangle paddle2 = new Rectangle(PREF_W - RECT_X - RECT_W,
STARTING_Y, RECT_W, RECT_H);
public PongPaddle() {
setBackground(Color.black);
new Timer(TIMER_DELAY, new TimerListener()).start();
}
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
private class TimerListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
int deltaPaddle1 = paddle1GoingDown ? 1 : -1;
deltaPaddle1 *= DELTA_PADDLE;
int x = paddle1.getLocation().x;
int y = paddle1.getLocation().y + deltaPaddle1;
if (y + RECT_H >= PREF_H) {
paddle1GoingDown = false;
}
if (y <= 0) {
paddle1GoingDown = true;
}
paddle1.setLocation(x, y);
int deltaPaddle2 = paddle2GoingDown ? 1 : -1;
deltaPaddle2 *= DELTA_PADDLE;
x = paddle2.getLocation().x;
y = paddle2.getLocation().y + deltaPaddle2;
if (y + RECT_H >= PREF_H) {
paddle2GoingDown = false;
}
if (y <= 0) {
paddle2GoingDown = true;
}
paddle2.setLocation(x, y);
repaint();
if (!PongPaddle.this.isShowing()) {
((Timer) e.getSource()).stop();
}
}
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.white);
if (paddle1 != null) {
g2.fill(paddle1);
}
if (paddle2 != null) {
g2.fill(paddle2);
}
}
private static void createAndShowGui() {
PongPaddle mainPanel = new PongPaddle();
JFrame frame = new JFrame("PongPaddle");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Key Listener isn't working

I've been experimenting with creating a java game but I've hit a roadblock, I can't get java to listen to any of my keys even when I'm just using print statements to test it out. From what I understand I've implemented KeyListener correctly and added the key listener to the Applet but it still isn't working.
My main class:
import java.awt.*;
import javax.swing.*;
public class Container extends JApplet implements Runnable {
private static final long serialVersionUID = 1L;
public static Dimension size = new Dimension(720,560); //Size of Screen
private static final int PIXELSIZE = 2;
public static Dimension pixel = new Dimension(size.width/PIXELSIZE,
size.height/PIXELSIZE); // Dimesions of screen in terms of pixels
public static final String NAME = "Game";
public static boolean isRunning = false;
private Image screen;
public static Level level;
public static MainCharacter p1;
public Container(){
setPreferredSize(size);
addKeyListener(p1);
}
public void start(){
new Tile();
level = new Level();
p1 = new MainCharacter(20,40);
isRunning = true;
new Thread(this).start();
}
public void tick(){
p1.tick();
}
public void render(){
Graphics g = screen.getGraphics();
g.setColor(new Color(130,160,255));
g.fillRect(0, 0, pixel.width, pixel.height);
level.render(g);
p1.render(g);
g = getGraphics();
g.drawImage(screen, 0, 0, size.width, size.height,
0, 0, pixel.width, pixel.height, null);
g.dispose();
}
public void run() {
screen = createVolatileImage(pixel.width,pixel.height);
while(isRunning){
tick();
render();
try{
Thread.sleep(5);
}catch(InterruptedException e){}
}
}
public static void main(String[] args){
Container container = new Container();
JFrame frame = new JFrame();
frame.add(container);
frame.pack();
frame.setTitle(NAME);
frame.setResizable(true);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
container.start();
}
public static void right(){
p1.right();
}
public static void left(){
p1.left();
}
}
My character class:
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class MainCharacter extends Tall implements KeyListener{
public double fallSpeed = 1.5;
public double moveSpeed = 1.0;
public double xSpeed = 1;
public MainCharacter(int width, int height){
setBounds(Container.pixel.width/2 - width/2,
Container.pixel.height/2 - height/2,
width, height);
}
public void tick(){
if(Container.level.space[(int)(x+width)][(int)(y+height)] &&
Container.level.space[(int)(x)][(int)(y+height)] &&
Container.level.space[(int)(x+width)][(int)(y)] &&
Container.level.space[(int)(x)][(int)(y)])
y += fallingSpeed;
}
public void render(Graphics g){
g.drawImage(Tile.tileset_terrain, (int)x, (int)y,
(int)(x+width),(int)(y+height),
Tile.CHARACTER[0]*Tile.TILE_SIZE,
Tile.CHARACTER[1]*Tile.TILE_SIZE,
Tile.CHARACTER[0]*Tile.TILE_SIZE +(int)width,
Tile.CHARACTER[1]*Tile.TILE_SIZE + (int)height, null);
}
public void right(){
x += xSpeed;
}
public void left(){
x -= xSpeed;
}
#Override
public void keyPressed(KeyEvent e) {
System.out.println("hey");
}
#Override
public void keyReleased(KeyEvent e) {
System.out.println("hey");
}
#Override
public void keyTyped(KeyEvent e) {
System.out.println("hey");
}
}

It looks like p1 is null when you add it as a KeyListener.
You add it as a KeyListener here:
public Container(){
setPreferredSize(size);
System.out.println(p1); // try this...
addKeyListener(p1);
}
But instantiate it here:
public void start(){
new Tile();
level = new Level();
p1 = new MainCharacter(20,40);
isRunning = true;
new Thread(this).start();
}

KeyListeners are fickle. They require that the component they are registered to are not only focusable, but have keyboard focus.
It's recommend that instead, you should use Key Bindings instead

How to make animation move its legs while moving?

So right now when you press go it just moves across the screen, but I also want it to move its legs so its doing something and not just standing still. Any tips on how to do that? I know it would be moving the 2nd leg pointers back and forth but I'm not sure how to do that
Class Stick2 :
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Stick2 extends JFrame implements ActionListener {
// Declares constants
public static final int FRAME_WIDTH = 500;
private static final int FRAME_HEIGHT = 500;
private static final int FRAME_X_ORIGIN = 150;
private static final int FRAME_Y_ORIGIN = 200;
private static final int BUTTON_WIDTH =80;
private static final int BUTTON_HEIGHT = 30;
JPanel buttonPanel, panel;
MovingBanner2 myBanner;
JButton startButton, stopButton;
Thread thrd;
public static void main(String[] args)
{
Stick2 frame = new Stick2();
frame.setVisible(true);
}
public Stick2(){
Container contentPane= getContentPane();
// Sets Frame
setSize(FRAME_WIDTH,FRAME_HEIGHT);
setResizable(false);
setTitle("Animation");
setLocation(FRAME_X_ORIGIN, FRAME_Y_ORIGIN);
// Sets layout manager
contentPane.setLayout(new BorderLayout(10,0));
buttonPanel = new JPanel();
JButton startButton = new JButton("Start");
startButton.setSize(BUTTON_WIDTH, BUTTON_HEIGHT);
buttonPanel.add(startButton);
startButton.addActionListener(this);
JButton stopButton = new JButton("Stop");
stopButton.setSize(BUTTON_WIDTH,BUTTON_HEIGHT);
buttonPanel.add(stopButton);
stopButton.addActionListener(this);
contentPane.add (buttonPanel, BorderLayout.SOUTH);
// Creates a balloon
myBanner = new MovingBanner2();
panel = myBanner;
panel.setBorder(BorderFactory.createLineBorder(Color.BLUE));
contentPane.add(panel, BorderLayout.CENTER);
}
public void actionPerformed (ActionEvent event){
JButton clickedButton = (JButton) event.getSource();
String buttonText = clickedButton.getText();
if (buttonText.equals("Stop")) {
myBanner.stopAnimation();
thrd = null;
}
else {
myBanner.startAnimation();
thrd = new Thread (myBanner);
thrd.start();
}
}
}
Class MovingBanner2:
class MovingBanner2 extends JPanel implements Runnable {
private int x;
private Boolean animate;
int bodyX = 250;
int bodyY1 = 160;
int bodyY2 = 210;
int armHeight = 190;
int armLength = bodyX + 30;
int armLength1 = bodyX - 30;
int legY = 340;
public MovingBanner2() {
x=10;
animate = true;
}
// Draws the String
public void paintComponent (Graphics g) {
super.paintComponent(g);
g.setColor(Color.RED);
//g.drawString("I love Java", x,50);
g.drawLine(bodyX + x, bodyY1, bodyX + x, bodyY2); //body
g.drawOval(bodyX + x - 15, bodyY1 - 40, 40, 40); //head
g.drawLine(armLength + x,armHeight, armLength1 + x, armHeight); //arms
g.drawLine(bodyX + x, bodyY2, bodyX + 20 + x,legY); //leg
g.drawLine(bodyX + x, bodyY2, bodyX - 20 + x, legY); //leg
}
public void run() {
while (animate) {
changeX();
repaint();
try {Thread.sleep(100); } catch(Exception e){};
}
}
public void changeX() {
if (x <= Stick2.FRAME_WIDTH - 240)
x++;
else x = 10;
}
public void stopAnimation() {
animate = false;
}
public void startAnimation() {
animate = true;
}
}

There are probably many answers to the question. The best I can come up with is basically to devise some kind of "cycle".
A cycle is a known period of time over which animation can run. In this example, it's 1 second.
You then need to provide a series of Animatable objects that are notified of a change to the cycle over time, which allows them to make changes accordingly. You can also ignore the cycle for those elements that don't need to cycle.
The intention is provide a single animation engine that can be responsible for updating the entire state in one go, rather then trying to use multiple threads/timers which may reduce the systems performance.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
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 TestAnimation06 {
public static void main(String[] args) {
new TestAnimation06();
}
public TestAnimation06() {
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 interface Animatable {
public void update(float progress);
}
public class AnimationEngine {
private List<Animatable> animations;
private int cycleTime = 1000;
private long startTime = -1;
public AnimationEngine() {
animations = new ArrayList<>(25);
Timer timer = new Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (startTime < 0) {
startTime = System.currentTimeMillis();
}
long duration = System.currentTimeMillis() - startTime;
float progress = (float)duration / (float)cycleTime;
if (duration >= cycleTime) {
progress = 1f;
startTime = System.currentTimeMillis();
}
for (Animatable animatable : animations) {
animatable.update(progress);
}
}
});
timer.setRepeats(true);
timer.setCoalesce(true);
timer.start();
}
public void add(Animatable animatable) {
animations.add(animatable);
}
}
public class TestPane extends JPanel {
private AnimationEngine engine;
public TestPane() {
setLayout(null);
engine = new AnimationEngine();
Legs legs = new Legs();
Walker walker = new Walker(legs);
engine.add(legs);
engine.add(walker);
walker.setSize(walker.getPreferredSize());
add(walker);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.dispose();
}
}
public class Walker extends JPanel implements Animatable {
private int speed = 2;
public Walker(Legs legs) {
setLayout(new GridBagLayout());
add(legs);
}
#Override
public void update(float progress) {
Container parent = getParent();
int width = parent.getWidth();
int xPos = getX() + speed;
if (xPos <= 0) {
speed *= -1;
xPos = 0;
} else if (xPos + getWidth() >= width) {
speed *= -1;
xPos = width - getWidth();
}
System.out.println(xPos);
setLocation(xPos, (parent.getHeight() - getHeight()) / 2);
repaint();
}
}
public class Legs extends JPanel implements Animatable {
private float frameProgress;
public Legs() {
setOpaque(false);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(25, 50);
}
#Override
public void update(float progress) {
frameProgress = progress;
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int width = getWidth();
int height = getHeight();
g.setColor(Color.BLACK);
g.drawLine(width / 2, 0, (int)(width * frameProgress), height);
g.drawLine(width / 2, 0, width - (int)(width * frameProgress), height);
}
}
}

Animating a Rectangle in Java

I've been trying to get this rectangle to move that I've created using a for loop. All that's happening with this code is that there is an original rectangle and then a new one next to that rectangle. No animation happens, only those two rectangles show on the window. What are some methods to get this rectangle to animate?
import java.awt.*;
import javax.swing.*;
public class Gunman extends JComponent {
/**
*
*/
private static final long serialVersionUID = 1L;
public int x = 10;
public int y = 10;
public int width = 8;
public int height = 10;
public void paint(Graphics g) {
g.setColor(Color.red);
g.drawRect (x, y, width, height);
g.fillRect (x, y, width, height);
for(int i = 0; i<=1024; i++){
g.setColor(Color.red);
g.drawRect(x++, y, width, height);
g.fillRect(x++, y, width, height);
}
}
}

Don't have program logic in a paint or paintComponent method, and by logic, I mean the for loop with "motion" as that just won't work. You want to
Almost never draw in a JComponent's paint method but rather in its paintComponent method.
Don't forget to call the super.paintComponent(g) method too, often as the first method call in the paintComponent(g) override.
Use a Swing Timer to step wise change the x and y values
call repaint() on the JComponent after the changes are made
For example
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Gunman extends JComponent {
private static final long serialVersionUID = 1L;
private static final int PREF_W = 900;
private static final int PREF_H = 700;
private static final int TIMER_DELAY = 30;
public int rectX = 10;
public int rectY = 10;
public int width = 8;
public int height = 10;
public Gunman() {
new Timer(TIMER_DELAY, new ActionListener() {
#Override
public void actionPerformed(ActionEvent actEvt) {
if (rectX < PREF_W && rectY < PREF_H) {
rectX++;
rectY++;
repaint();
} else {
((Timer)actEvt.getSource()).stop();
}
}
}).start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.red);
g.drawRect(rectX, rectY, width, height);
g.fillRect(rectX, rectY, width, height);
}
public int getRectX() {
return rectX;
}
public void setRectX(int rectX) {
this.rectX = rectX;
}
public int getRectY() {
return rectY;
}
public void setRectY(int rectY) {
this.rectY = rectY;
}
private static void createAndShowGui() {
Gunman mainPanel = new Gunman();
JFrame frame = new JFrame("Gunman");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

There are numerous ways to animate. Here is another example. Notice the location of repaint() inside a background thread. This paints directly on a JFrame. Use paintComponent() when painting on JPanels.
public static void main(String args[]) throws Exception {
new JFrame("Draw a red box") {
Point pointStart = new Point(50,50);
Point pointEnd = new Point(200,200);
public void paint(Graphics g) {
super.paint(g);
if (pointStart != null) {
g.setColor(Color.RED);
g.drawRect(pointStart.x, pointStart.y, pointEnd.x, pointEnd.y);
}}{
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
setSize(300, 300);
setLocation(300, 300);
setVisible(true);
Thread t = new Thread(new Runnable() {
public void run() {
while (pointEnd.x > 0 && pointEnd.y > 0) {
pointEnd = new Point(--pointEnd.x, --pointEnd.y);
repaint();
try {
Thread.sleep(22);
} catch (InterruptedException e) {
e.printStackTrace();
}}
pointStart = null;
pointEnd = null;
}});
t.setDaemon(true);
t.start();
}};}

UPDATE: Ok previous answer was not so good from the old memory, here is the quickest, cheapest, most dirty way to get some animation quicksmart, you can copy and compile the code as is:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JFrame;
public class Test extends JFrame {
public Gunman g = new Gunman();
public static void main( String[] args ) {
Test t = new Test();
t.setSize( 800, 600 );
t.setVisible( true );
t.getContentPane().add( t.g );
while ( true ) {
t.g.x = t.g.x + 1;
t.g.y = t.g.y + 1;
t.repaint();
try {
Thread.sleep( 100 );
} catch ( InterruptedException e ) {
}
}
}
public void paintComponent( Graphics g ) {
g.clearRect( 0, 0, 800, 600 );
}
}
class Gunman extends JComponent {
private static final long serialVersionUID = 1L;
public int x = 10;
public int y = 10;
public int width = 8;
public int height = 10;
public void paintComponent( Graphics g ) {
g.setColor( Color.red );
g.fillRect( x, y, width, height );
}
}
There are ALOT of shortcuts in this, as Hovercraft of Eels has said, this is not an 'ideal' way to do it, but it has the basic structure. You have a canvas (I have used the JFrame, again not really recommended), and you add a component to it. You must override paintComponent (if you are using swing, which I do recommend you do), and this will draw your component.
You then need to alter your component's position in some way (recommend a proper method call on the object that does this), and ask the canvas to repaint itself.
I have included the wait so you can see what's happening, but if you are thinking of game programming, you should look into creating a game loop to manage this, I recommend Killer game programming in java, you can get a free ebook version with a quick google search.