Major help needed with drawing rectangles using JFrame and Mouse Events

Good evening!

So, I've been working on this program that draws rectangles using JFrame and implementing MouseListener and MouseMotionListener. You should be able to click and drag the mouse, drawing a rectangle, no matter where in the frame you start out. I have not had much luck getting it to work. The frame will display, but I am unable to draw the rectangles. It also produces one error when I compile, "JDrawRect.java:81: cannot find symbol symbol : method paintComponent(java.awt.Graphics) location: class javax.swing.JFrame super.paintComponent(g);". When the program runs, in addition to the frame loading, there is an additional error, "Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container".

What am I doing wrong?

Damien

Code:

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package project2;

// JDrawRect.java
// Demonstrating mouse events.
  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;

    public class JDrawRect extends JFrame
    implements MouseListener, MouseMotionListener {
  //imported variables follow...
      private int pointCount = 0;
      private Point points[]  = new Point[100];
      private Point points2[] = new Point[100];
      private Point start = new Point();
      private Point end  = new Point();
      Rectangle rect = new Rectangle();
  //imported variables end
 
  //private static final long serialVersionUID = 1L;
      private JLabel mousePosition;
 
  // set up GUI and register mouse event handlers
      public JDrawRect()
      {
        super( "Drawing Rectangles" );
   
        mousePosition = new JLabel();
        mousePosition.setHorizontalAlignment(SwingConstants.CENTER);
        getContentPane().add( mousePosition, BorderLayout.CENTER );
   
       
        addMouseListener( this );        // listens for own mouse and
        addMouseMotionListener( this );  // mouse-motion events
   
        //setSize( 400, 300 );
        //setVisible( true );
      }
 
  // MouseListener event handlers
  // handle event when mouse released immediately after press
      public void mouseClicked( MouseEvent event ){}
 
  // handle event when mouse pressed
      public void mousePressed( MouseEvent event )
      {
        start = event.getPoint();
      }
 
  // handle event when mouse released after dragging
      public void mouseReleased( MouseEvent event )
      {
        points[pointCount] = start;
        points2[pointCount] = event.getPoint();
        pointCount++;
        rect.setFrameFromDiagonal(start, start);
        repaint();
      }
 
  // handle event when mouse enters area
      public void mouseEntered( MouseEvent event ){}
 
  // handle event when mouse exits area
      public void mouseExited( MouseEvent event ){}
 
  // MouseMotionListener event handlers
  // handle event when user drags mouse with button pressed
      public void mouseDragged( MouseEvent event )
      {
        end = event.getPoint();
        rect.setFrameFromDiagonal(start, end);
        repaint();
      }
 
  // handle event when user moves mouse
      public void mouseMoved( MouseEvent event ){}
 
 
      public void paintComponent(Graphics g)
      {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        // Draw line being dragged.
        g2.setPaint(Color.red);
        g2.draw(rect);
        // Draw lines between points in arrays.
        g2.setPaint(Color.blue);
        Rectangle r = new Rectangle();
        for (int i =0; i < pointCount; i++)
        {
            r.setFrameFromDiagonal(points[i], points2[i]);
            g2.fill(r);
        }
      }
      public static void main( String args[] )
      {
        //JDrawRect application = new JDrawRect();
        //application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   
        JDrawRect test = new JDrawRect();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(test);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
   
      }
 
  } // end class JDrawRect

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For one thing, you're trying to draw in the JFrame itself and trying to override a non-existent method, paintComponent. JFrames don't have a paintComponent method since they do not inherit from JComponent. To find out for yourself, just place an @Override annotation above your paintComponent method and see that it will cause an error:

Code:

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  @Override  // this causes a compile error
  public void paintComponent(Graphics g) {
  //...

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This is the same reason that calling super.paintComponent(g) fails here as there simply is no super for this method in a JFrame.

Far better is to do the drawing in a JPanel or JComponent, and override paintComponent in this class. Then create an instance of this and place it in your JFrame's contentPane. The Sun Swing graphics tutorial should explain this in more detail and is required reading I should think.

Other suggestions:
1) Don't have your main drawing class implement MouseListener and MouseMotionListener. Instead I'd create a private inner class that extends MouseAdapter.
2) Instead of a fixed array of 100 Point objects, consider using the more flexible ArrayList<Point>, or perhaps even ArrayList<Rectangle2D>

For instance,

Code:

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import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.List;

import javax.swing.*;

public class JDrawRect2 extends JPanel {
  private static final Color RECT_FILL_COLOR = Color.blue.brighter().brighter();
  private static final Color RECT_DRAW_COLOR = Color.blue.darker();
  private static final Color DRAGGING_RECT_COLOR = Color.pink;
  private static final Dimension MAIN_SIZE = new Dimension(800, 600);
  private List<Rectangle2D> rectList = new ArrayList<Rectangle2D>();
  private Rectangle2D draggingRect = null;
 
  public JDrawRect2() {
    setPreferredSize(MAIN_SIZE);
    MouseAdapter mouseAdapter = new MyMouseAdapter();
    addMouseListener(mouseAdapter);
    addMouseMotionListener(mouseAdapter);
  }
 
  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
   
    Graphics2D g2 = (Graphics2D)g;
    for (Rectangle2D rect : rectList) {
      g2.setColor(RECT_FILL_COLOR);
      g2.fill(rect);
      g2.setColor(RECT_DRAW_COLOR);
      g2.draw(rect);
    }
    if (draggingRect != null) {
      g2.setColor(DRAGGING_RECT_COLOR);
      g2.draw(draggingRect);     
    }
  };
 
  // in case the MouseAdapter is not an inner class
  public void addRectangle(Rectangle2D r) {
    rectList.add(r);
  }
 
  public void setDraggingRect(Rectangle2D r) {
    draggingRect = r;
  }
 
  private class MyMouseAdapter extends MouseAdapter {
    private Point start = null;
   
    @Override
    public void mousePressed(MouseEvent e) {
      start = e.getPoint();
    }
   
    @Override
    public void mouseReleased(MouseEvent e) {
      addRectangle(createRect2D(e));
      setDraggingRect(null);
      JDrawRect2.this.repaint();
    }
   
    @Override
    public void mouseDragged(MouseEvent e) {
      setDraggingRect(createRect2D(e));
      JDrawRect2.this.repaint();     
    }

    private Rectangle2D createRect2D(MouseEvent e) {
      Point end = e.getPoint();
      int width = Math.abs(start.x - end.x);
      int height = Math.abs(start.y - end.y);
      int x = Math.min(start.x, end.x);
      int y = Math.min(start.y, end.y);
      Rectangle2D r = new Rectangle2D.Double(x, y, width, height);
      return r;
    }
  }

  private static void createAndShowUI() {
    JFrame frame = new JFrame("JDrawRect2");
    frame.getContentPane().add(new JDrawRect2());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        createAndShowUI();
      }
    });
  }
}

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