ADVANCED GUIS AND GRAPHICS - Java Programming: From Problem Analysis to Program Design - page 854

EXAMPLE 12-10

The program in this example shows how to handle the mouse-dragged event. You can
handle the mouse moved event similarly. These events are handled by the interface
MouseMotionListener , which contains the methods mouseDragged and mouseMoved ,
which, in turn, are used to handle the mouse-dragged and mouse-moved events,
respectively.
The program starts with some colored dots. If you drag a dot using the mouse, the dot
turns into a line. This way, you can ''freehand draw'' different pictures. What is really
happening is that we created small circle objects. The program contains the method
selected to check whether or not the mouse is on a circle. If you drag a circle, the
method mouseDragged is invoked and it paints a new circle. The sequence of circles
gives the impression of drawing a line. The complete program listing follows:
import javax.swing.*;
import java.awt.event.*;
import java.applet.*;
import java.awt.*;

public class FreeDrawApplet extends JApplet
implements MouseMotionListener

{

//instance variables
ColorCircle[] myGraph;

final int NUM_CIRCLES = 7;
final int WIDTH = 400;
final int HEIGHT = 400;
public class ColorCircle
{

private int x;
private int y;
public void setX( int iNewX)
{

x = iNewX;

}

public void setY( int iNewY)
{

y = iNewY;

}

public void paint (Graphics g)
{

g.fillOval(x - 10, y - 10, 20, 20);

}