The general way to do most Swing drawing is via passive graphics. This means:
- Do the drawing itself in the
paintComponent(Graphics g)
method of a JPanel or JComponent. - In your MouseListener change the state of some of the fields of the class. In your
mouseClicked
method you are setting the state of some local variables, and I recommend that you instead make your x and y fields, not local. - Then when the mouse listener is done making changes, call
repaint()
on the JPanel. - Then in the paintComponent method, use those fields that were changed in the mouse listener to do your drawing.
- Don't forget to call the super's paintComponent method in your paintComponent override.
- Don't forget to read tutorials on Swing Graphics to get the fine points.
Edit
For example, please have a look at a small graphics program that I created for an answer to another recent question.
The drawing occurs in the main class, SpaceShip, which extends JPanel. I add an anonymous inner MouseAdapter class for my Mouse Listener, and inside of the MouseAdapter, I call a method called moveIt, passing in the MouseEvent object.
MouseAdapter myMouseAdapter = new MouseAdapter() {
public void mousePressed(MouseEvent evt) {
moveIt(evt);
count = count + 1;
}
@Override
public void mouseDragged(MouseEvent evt) {
moveIt(evt);
}
};
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
All moveIt(MouseEvent evt)
does is to change the state of two fields, myX and myY, and then calls repaint()
on the current class:
public void moveIt(MouseEvent evt) {
myY = evt.getY() - sprite.getHeight() / 2;
myX = evt.getX() - sprite.getWidth() / 2;
repaint();
}
And then in the class's paintComponent
method, I first call the super's paintComponent to allow it to erase any previous old out of date images, then I paint a background image, background, then I draw a sprite that uses the myX and myY variables to tell it where to draw, then I draw some yellow rectangles at locations that are determined by the JPanel's size:
protected void paintComponent(Graphics g) {
super.paintComponent(g);
font1 = new Font("Serif", Font.BOLD, 36);
g.drawImage(background, 0, 0, this);
g.drawImage(sprite, myX, myY, this);
g.setColor(Color.yellow);
int rectCount = 10;
int height = getHeight() / rectCount;
int width = 272;
int x = getWidth() - width;
for (int i = 0; i < rectCount; i++) {
int y = i * height;
g.drawRect(x, y, width, height);
}
g.setFont(font1);
g.drawString(Integer.toString(count), 500, 100);
}
The whole thing looks like this:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.awt.Graphics;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.io.IOException;
import java.net.URL;
import java.lang.String;
import java.awt.Font;
@SuppressWarnings("serial")
public class SpaceShip extends JPanel {
private static final String BACKGROUND_PATH = "http://www.thatsreallypossible.com/"
+ "wp-content/uploads/2012/12/Space-Colonialisation.jpg";
private static final String SPRITE_PATH = "http://www.pd4pic.com/"
+ "images250_/ufo-flying-saucer-spacecraft-spaceship-alien.png";
private Font font1;
int myX = 100;
int myY = 400;
int count = 0;
private BufferedImage background;
private BufferedImage sprite;
public SpaceShip() throws IOException {
URL backgroundUrl = new URL(BACKGROUND_PATH);
URL spriteUrl = new URL(SPRITE_PATH);
background = ImageIO.read(backgroundUrl);
sprite = ImageIO.read(spriteUrl);
MouseAdapter myMouseAdapter = new MouseAdapter() {
public void mousePressed(MouseEvent evt) {
moveIt(evt);
count = count + 1;
}
@Override
public void mouseDragged(MouseEvent evt) {
moveIt(evt);
}
};
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
@Override
public Dimension getPreferredSize() {
if (background != null) {
return new Dimension(background.getWidth(), background.getHeight());
}
return super.getPreferredSize();
}
public void moveIt(MouseEvent evt) {
myY = evt.getY() - sprite.getHeight() / 2;
myX = evt.getX() - sprite.getWidth() / 2;
repaint();
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
font1 = new Font("Serif", Font.BOLD, 36);
g.drawImage(background, 0, 0, this);
g.drawImage(sprite, myX, myY, this);
g.setColor(Color.yellow);
int rectCount = 10;
int height = getHeight() / rectCount;
int width = 272;
int x = getWidth() - width;
for (int i = 0; i < rectCount; i++) {
int y = i * height;
g.drawRect(x, y, width, height);
}
g.setFont(font1);
g.drawString(Integer.toString(count), 500, 100);
}
public static void main(String[] args) {
JFrame frame = new JFrame("Basic Game");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
SpaceShip ex;
try {
ex = new SpaceShip();
frame.getContentPane().add(ex);
frame.pack();
frame.setResizable(false);
frame.setVisible(true);
ex.requestFocus();
} catch (IOException e) {
e.printStackTrace();
}
}
}