In this tutorial, I will show you how to use java swing to make a simple painting application. We will learn two basic operations: Implementing MouseListener and overriding paint method.
The application will consist of two classes. Our first class will extend JFrame and the second one will be a JPanel class to be added to the first class. All the painting staff will be handled in our JPanel class.
We will create paintings by drawing lines between the points that mouse is clicked on. Here are the classes:
Main.java:
package paint;
import javax.swing.JFrame;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public class Main extends JFrame {
public Main(){
super("Painting Application");
setSize(400, 500);
setVisible(true);
addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e){
System.exit(0);
}
});
add(new MyPanel());
}
public static void main(String[] args) {
new Main();
}
}
MyPanel.java:
package paint;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JPanel;
public class MyPanel extends JPanel{
MouseMotionListener theListener;
Graphics g;
MouseListener theListening;
int x,y,x1,y1;
boolean inside;
public MyPanel(){
x=0; y=0; x1=-99; y1=-99;
inside=false;
theListener=new MouseMotionListener() {
public void mouseDragged(MouseEvent arg0) {
if(inside){
repaint();
}
}
public void mouseMoved(MouseEvent arg0) {
}
};
theListening=new MouseListener() {
public void mouseClicked(MouseEvent arg0) {
//Nothing to be done…
}
public void mousePressed(MouseEvent arg0) {
//Nothing to be done…
}
public void mouseReleased(MouseEvent arg0) {
x1=-99;y1=-99;//Mouse released. We need to make sure no last point for future use.
}
public void mouseEntered(MouseEvent arg0) {
inside=true; //Mouse has just entered
x1=-99;y1=-99; //No last point because the mouse was outside.
}
public void mouseExited(MouseEvent arg0) {
inside=false; //Mouse is now outside
x1=-99; y1=-99; //No last point, mouse is outside
}
};
this.setSize(400,500);
this.setVisible(true);
this.addMouseMotionListener(theListener);
this.addMouseListener(theListening);
}
@Override
public void paint(Graphics g){
try{
if(x1==-99){ // if x equals to -99 then y also equals to -99. A point of (-99,-99) is not possible so nothing will be drawn.
x=getMousePosition().x; x1=x; //Getting the point so that we will be able to use it as the first point
y=getMousePosition().y; y1=y; //of the line when another point is clicked.
}
else//Event just occurred at (x1,y1). Between (x,y) and (x1,y1) a line will be drawn
{
x=getMousePosition().x;
y=getMousePosition().y;
g.drawLine(x, y, x1, y1);
x1=x; y1=y;
}
}
catch(Exception ex){
}
}
}
If you have any problem running or understanding the code please give me feedback.
