Drawing a line on canvas in Java ME

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This code snippet demonstrates how to draw lines in a Java ME MIDlet.

Article Metadata

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Code Example

Source file: Media:DrawingLine.zip Media:DrawingLine.diff.zip

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Tested with

SDK: Nokia SDK 1.1 for Java, Nokia SDK 2.0 for Java (beta), Nokia Symbian SDKs

Devices(s): Nokia E70, Nokia 5800 XpressMusic, Nokia 6021, Nokia 6131, Nokia C3-01, Nokia E7-00, Nokia Asha 206

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Compatibility

Platform(s): Series 40, Symbian

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Article

Keywords: javax.microedition.lcdui.Canvas, javax.microedition.lcdui.Graphics, javax.microedition.lcdui.Canvas.paint, javax.microedition.lcdui.Graphics.drawLine

Created: dekudin (26 Feb 2009)

Last edited: hamishwillee (02 Oct 2012)

Overview

The Canvas class is used for drawing lines and other simple graphics. Since Canvas is an abstract class, in order to draw lines, you must implement your own class based on Canvas and implement the paint method which is used for drawing on the canvas. After that, this class may be used as displayable - it can be assigned as the current displayable and it can contain commands.

This MIDlet consists of 2 source files:

1. DrawingLineMidlet.java - contains the MIDlet class.
2. DrawingLineCanvas.java - contains the DrawingLineCanvas class, with implemented method paint which is used to draw a line.

Source file: DrawingLineMidlet.java

    // Canvas for drawing line
    private DrawingLineCanvas canvas;
 
    public DrawingLineMidlet() {
        setupCanvas();
    }
 
    /**
     * Sets up canvas for drawing line.
     */
    private void setupCanvas() {
        canvas = new DrawingLineCanvas();
        canvas.setTitle("Drawing the line");
 
        canvas.addCommand(EXIT_COMMAND);
        canvas.setCommandListener(this);
    }
 
    /**
     * From MIDlet.
     * Called when the MIDlet is started.
     */
    public void startApp() {
        // The initial display is the main form
        Display.getDisplay(this).setCurrent(canvas);
    }

Source file: DrawingLineCanvas.java

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Graphics;
 
/**
 * Canvas for drawing line.
 */
public class DrawingLineCanvas extends Canvas {
    // Draw a diagonal black line
    protected void paint(Graphics g) {
        g.drawLine(10, 10, getWidth() - 10, getHeight() - 10);
    }
}

Postconditions

A canvas with a diagonal black line on a white background is drawn on the display.

Supplementary material

This code snippet is part of the stub concept, which means that it has been patched on top of a template application in order to be more useful for developers. The version of the Java ME stub application used as a template in this snippet is v1.1.

• The patched, executable application that can be used to test the features described in this snippet is available for download at Media:DrawingLine.zip.
• You can view all the changes that are required to implement the above-mentioned features. The changes are provided in unified diff and colour-coded diff (HTML) formats in Media:DrawingLine.diff.zip.
• For general information on applying the patch, see Using Diffs.
• For unpatched stub applications, see Example app stubs with logging framework.