Introduction to J2ME

// **********FirstOne.java************
 
Package FirstOne;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
 
public class FirstOne extends MIDlet implements CommandListener
{
// The canvas is the region of the screen that has been allotted to the game. 
 
	FirstCanvas myCanvas; 
	private Command exitCommand = new Command("Exit", Command.EXIT, 99);
	private Command changeCommand = new Command("changeMessage ", Command.SCREEN, 1);
 
// Initialize the canvas and the commands.
 
	public FirstOne() 
	{
	  myCanvas = new FirstCanvas();  
	  myCanvas.addCommand(exitCommand);
	  myCanvas.addCommand(changeCommand);
 
	// Set one command listener to listen to all of the commands on the canvas  
 
	  myCanvas.setCommandListener(this);
	}
 
	public void startApp() throws MIDletStateChangeException
	 {
	// display my canvas on the screen:
	  Display.getDisplay(this).setCurrent(myCanvas);  
	  myCanvas.repaint();
	}
 
// If the MIDlet was using resources, it should release them in this method.
 
	public void destroyApp(boolean unconditional) 
	    throws MIDletStateChangeException { }
 
 //MIDlet enters a paused state. The MIDlet should release shared resources. 
 
	public void pauseApp() {  }
 
//Respond to a command. Either reset or exit.
 
	public void commandAction(Command c, Displayable s) 
	{
		  if(c == changeCommand) 
		{
		    myCanvas.changeFirst();
		} 
		else if(c == exitCommand) 
		{ 
		    try {
		      destroyApp(false);
		      notifyDestroyed();
		    } catch (MIDletStateChangeException ex){  }
		}
	 }
}
 
// *************FirstCanvas.java.***************
 
package FirstOne;
import javax.microedition.lcdui.*;
//This class represents the region of the screen that has been allotted.
 
public class FirstCanvas extends Canvas 
{
	boolean firstDisp = true;
 
//Change the display message.
 
	void changeMsg() 
	{
	  firstDisp = !firstDisp;
	  repaint();
	}
 
//clear the screen and display the " Hi This is My First Program " message.
 
	public void paint(Graphics g) 
	{
 
	// get the dimensions of the screen:
	  int width = getWidth ();
	  int height = getHeight();
 
	// clear the screen. Setting Screen Color to white:
	  g.setColor(0xffffff);	  
	  g.fillRect(0, 0, width, height);
 
	// display the " Hi This is My First Program " message if appropriate:.
		if(firstDisp) 
		{
		    Font font = g.getFont();
		    int fontHeight = font.getHeight();
		    int fontWidth = font.stringWidth("Hi This is My First Program ");
		// set the text color
		    g.setColor(255, 255, 0);
		    g.setFont(font);
 
		// write the string in the center of the screen
		    g.drawString("Hi This is My First Program ", (width - fontWidth)/2,   
		                  (height - fontHeight)/2,g.TOP|g.LEFT);
		}
	}
}