sketcher.java


package sketcher;

import java.awt.*;
import java.awt.event.*;
import java.util.Vector;

public class Sketcher  extends Frame {

    public SketchCanvas canvas;
    
    public Vector<PointPair> points_;
    
    public Sketcher() {
        setSize(500,500);
        setTitle("Sketch Pad");
        canvas = new SketchCanvas();
        add(canvas,"Center");
    }

    public static void main(String[] args) {
        Sketcher frame = new Sketcher();
        frame.points_ = new Vector<PointPair>();
        WindowWatcher w = new WindowWatcher();
        MouseWatcher mw = new MouseWatcher( frame.points_);
        frame.canvas.addMouseListener(mw);
        frame.canvas.addMouseMotionListener(mw);
        frame.setVisible(true);
        frame.addWindowListener(w);
    }
    
    public void repaint() {
        Graphics g = this.canvas.getGraphics();
        for(int i = 0;i <  points_.size();i++){
            g.drawLine(points_.get(i).start.x, points_.get(i).start.y, points_.get(i).end.x, points_.get(i).end.y);
        }
        g.dispose();
    }
    
    public void paint() {
    
    }
    
    public void paint(Graphics g) {
        
    }
    
    public void repaint(Graphics g) {
    }
}



sketchercanvas.java

package sketcher;

import java.awt.*;
public class SketchCanvas extends Canvas {
    public void repaint() {
    }
    
    public void paint() {
    
    }
    
    public void paint(Graphics g) {
        
    }
    
    public void repaint(Graphics g) {
    }
}



mousewatcher.java

package sketcher;


import java.awt.*;
import java.awt.event.*;
import java.util.Vector;


public class MouseWatcher extends MouseAdapter implements MouseMotionListener {

    private Point currentPoint, oldPoint;
    
    private Vector<PointPair> points_;
    
    public MouseWatcher(Vector<PointPair> points) {
        points_ = points;
    }

    public void mousePressed(MouseEvent e) {
        oldPoint = e.getPoint();
    }
    
    public void mouseReleased(MouseEvent e) {
        
    }
    
    public void mouseDragged(MouseEvent e) {
        currentPoint = e.getPoint();
        
        Graphics g = ((Canvas)e.getSource()).getGraphics();
        
        g.drawLine(oldPoint.x, oldPoint.y, currentPoint.x, currentPoint.y);
        
        
        
        points_.add(new PointPair(oldPoint, currentPoint));
        
        oldPoint = currentPoint;
        g.dispose();
    }
    
    
    public void mouseMoved(MouseEvent e) {}

}



windowwatcher.java

package sketcher;

import java.awt.*;
import java.awt.event.*;

public class WindowWatcher extends WindowAdapter {
    public void windowClosing(WindowEvent e) {
        System.exit(0);
    }
    
    public void windowDeactivated(WindowEvent e) {
        e.getWindow().repaint();
    }
    
    public void windowActivated(WindowEvent e) {
        e.getWindow().repaint();
    }
    
}


pointpair.java

package sketcher;

import java.awt.*;

public class PointPair {
    public Point start;
    public Point end;
    
    public PointPair(Point start_, Point end_){
        start = start_;
        end = end_;
    }
}