Graphics Methods in Java

Drawing Lines

The drawLine method belongs to the Graphics class.

This example draws a fan of twenty lines from the bottom center of the Applet along the top edge. The applet's getSize method is used to find the dimensions of the applet.

Code:

import java.awt.*;
import java.applet.*;
public class LineExample extends Applet
{
    public LineExample()
    {
        this.setBackground(new Color(255, 255, 255));
        this.setForeground(new Color(255, 0, 0));
    }
    public void paint(Graphics g)
    {
        // Get the width and height of the Applet
        int width = this.getSize().width;
        int height = this.getSize().height;
        // Fan 20 lines from the bottom-middle, across the top
        for (int counter=0; counter<=width; counter+=(width/20))
            g.drawLine(width/2, height, counter, 0);
    }
}

Drawing Ovals

The drawOval method belongs to the Graphics class.

The drawOval method takes four parameters; x, y, width, and height. The following example draws an oval, half the size of the applet, in the center of the applet.

Code:

import java.awt.*;
import java.applet.*;
public class OvalExample extends Applet
{
    public OvalExample()
    {
        this.setBackground(new Color(255, 255, 255));
        this.setForeground(new Color(255, 0, 0));
    }
    public void paint(Graphics g)
    {
        // Get the width and height of the Applet
        int width = this.getSize().width;
        int height = this.getSize().height;
        g.drawOval(width/4, height/4, width/2, height/2);
    }
}

Freehand Drawing

In the previous examples, the paint method was used to display graphics on the applet. The paint method has a parameter for the graphics context, but you may wish to use the graphics context in other methods that don't have a graphics parameter. The getGraphics method is used to return the graphics context for a component, which in this case is the applet.

Graphics g = this.getGraphics();

Freehand Example:

The following example uses the getGraphics method for free-hand drawing. The example uses a MouseListener, and a MouseMotionListener, which are part of the Java 1.1 Event Model.

Code:

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class FreehandExample extends Applet implements MouseListener, MouseMotionListener
{
    private Point start, end;
    public FreehandExample()
    {
        this.setBackground(new Color(255, 204, 0));
        this.setForeground(new Color(51, 153, 204));
        // Add the Event Listeners
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
    }
    // Capture the mousePressed event
    public void mousePressed(MouseEvent e)
    {
        start = new Point(e.getX(), e.getY());
    }
    // Define the other events for MouseListener
    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
	
    // Capture the mouseDrag event
    public void mouseDragged(MouseEvent e)
    {
        // Get the current state of the graphics
        Graphics g = this.getGraphics();
		
        end = new Point(e.getX(), e.getY());
        g.drawLine(start.x, start.y, end.x, end.y);
        start = end;
    }
    // Define the other events for MouseMotionListener
    public void mouseMoved(MouseEvent e) {}
}