Converting an App to Applet

[josephdcoleman]

I am having a problem converting an old paint program to an applet. I can get it to compile and run, but when the applet window comes up it is blank. Thanks for any help.

/**
 * @(#)TestApplet2.java
 *
 * TestApplet2 Applet application
 *
 * @author 
 * @version 1.00 2009/2/20
 */
 
import java.awt.*;
import java.applet.*;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.JApplet;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseMotionAdapter;

public class TestApplet2 extends JApplet {
	
   private int pointCount = 0; // count number of points

   // array of 2 java.awt.Point references
   private Point points[] = new Point[ 2 ];  
   
   private boolean p0Exists = false; 
   private boolean p1Exists = false; 
   private int r = 8;
	
	public void init() {
		
		JFrame mainframe = new JFrame();
		TestApplet2 paintPanel = new TestApplet2();
		mainframe.add(paintPanel, BorderLayout.CENTER);
		
		JPanel bottomPanel = new JPanel();
		
		//label 1
		JLabel label1 = new JLabel("1. Click in two Locations.");
		label1.setBackground(Color.CYAN);
		label1.setOpaque(true);
		bottomPanel.add(label1, BorderLayout.SOUTH); //add label to JPanel
		
		//label 2
		JLabel label2 = new JLabel("2. Drag the points.");
		label2.setBackground(Color.YELLOW);
		label2.setOpaque(true);
		bottomPanel.add(label2, BorderLayout.SOUTH);
		
		mainframe.add(bottomPanel, BorderLayout.SOUTH);
	}
	
	public TestApplet2()
	{
		super();
		this.setBackground( Color.WHITE );
		
		// handle frame mouse  event
		addMouseListener(
		
			new MouseAdapter() // anonymous inner class
			{  
				// define a point and repaint
				public void mousePressed( MouseEvent event )
				{
					if ( !p0Exists ) 
					{
						// create point0
						points[ 0 ] = new Point( event.getX(), event.getY() ); 
						//System.out.println("Point 0 created: " + points[ 0 ] );
						p0Exists = true;
						repaint();	
					} else if ( !p1Exists ) 
					{
						// create point1
						points[ 1 ] = new Point( event.getX(), event.getY() ); 
						//System.out.println("Point 1 created: " + points[ 1 ] );
						p1Exists = true;
						repaint();	
					}
				
				} // end method mousePressed
				
			} // end anonymous inner class
		); // end call to addMouseMotionListener
		
		// handle frame mouse motion event
		addMouseMotionListener(
		
			new MouseMotionAdapter() // anonymous inner class
			{  
				// drag the point and repaint
				public void mouseDragged( MouseEvent event )
				{
					//System.out.println("Mouse dragged: x=" + event.getX() + "  y=" + event.getY() );
					if ( p0Exists ) 
					{
						if ( Math.abs(points[ 0 ].x - event.getX()) < r 
							&& Math.abs(points[ 0 ].y - event.getY()) < r ) 
						{
							// set new coordinates for point0
							points[ 0 ] = new Point( event.getX(), event.getY() ); 
							repaint();	
						}
					} 
					if ( p1Exists ) 
					{
						if ( Math.abs(points[ 1 ].x - event.getX()) < r 
							&& Math.abs(points[ 1 ].y - event.getY()) < r ) 
						{
							// set new coordinates for point1
							points[ 1 ] = new Point( event.getX(), event.getY() ); 
							repaint();	
						}
					}					
				} // end method mouseDragged
			} // end anonymous inner class
		); // end call to addMouseMotionListener
	} // end TestApplet2 constructor

	// draw oval in a 4-by-4 bounding box at specified location on window
	public void paintComponent( Graphics g )
	{
		this.paintComponent( g ); // clears drawing area
		if ( p0Exists ) 
		{
			g.drawOval( points[ 0 ].x - r/2, points[ 0 ].y - r/2, r, r );
			g.drawString("Point0", points[ 0 ].x, points[ 0 ].y - 3*r );
			g.drawString("x=" + points[ 0 ].x + " y=" + points[ 0 ].y, 
										points[ 0 ].x, points[ 0 ].y - r );
		}
		if ( p1Exists ) 
		{
			g.drawOval( points[ 1 ].x - r/2, points[ 1 ].y - r/2, r, r );
			g.drawString("Point1", points[ 1 ].x, points[ 1 ].y - 3*r );
			g.drawString("x=" + points[ 1 ].x + " y=" + points[ 1 ].y, 
										points[ 1 ].x, points[ 1 ].y - r );
		}
	} // end method paint
	
} // end class TestApplet2

[Fubarable]

You need to read up more on how to create applets as yours I'm afraid is completely mixed up. You appear to be creating a new object of your applet class in its init method -- not a good thing to do, and then try to add this pseudo-applet object to the contentPane of a JFrame -- an even worse thing to do. You can't band-aid these two beasts together like this.

Then your class that creates the JApplet has a constructor which is probably not what you want to do.

What you likely want is a class that creates a GUI JPanel that has a constructor and all. Then I'd have a separate class with an init method that extends JApplet and would add a newly created JPanel GUI to the JApplet's contentPane. Get rid of all references to JFrames, and most importantly, read the tutorial on how to make applets.

Best of luck.

edit: also your paintComponent method currently will do nothing since it's not held in a class that will call this as an override when the JVM calls paint. It's a good idea to use an @Override annotation here to see if the method you've created is actually overriding an existing method (as it should be doing).