calling paint from another class

[Vinod Venugopal]

hi ,
simple problem but cant rack my brains enuf :-)
Ok, now I have 2 classes which extends from JPanel each, one of them ( p1) has a button draw, once I click on draw I should be able to draw a line in the other panel ( p2) but without creating an object of p2, how do I do it?
for eg.
class p1 extends JPanel
{
}
class p2 extends JPanel
{
draw.addAction...
{
//draw line in p1 ..
});
}

[Dirk Schreckmann]

On Tony Alicea's Java Page you'll find a demonstration of Inter-Applet Communication.
Good Luck.

[Manfred Leonhardt]

Hi Vinod,
If you have common parents the problem is quite easy. You can just get the parent and then use the sibling object array to get a handle on the other panel. The code below shows an example.

  
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class MyPanel1 extends JPanel
{
  public void paintComponent( Graphics g )
  {
    super.paintComponent( g );
    System.out.println( "Painting one MyPanel1." );
  }
}
class MyPanel2 extends JPanel
{
  public MyPanel2()
  {
    JButton b = new JButton( "Hit Me" );
    b.addActionListener(
      new ActionListener()
      {
        public void actionPerformed( ActionEvent ae )
        {
          someMethod();
        }
      });
    add( b );
  }
  public void someMethod()
  {
    Container parent = getParent();
    Object[] siblings = parent.getComponents();
    //
    // I know that first child is one I want.
    //
    if( siblings[0] instanceof MyPanel1 )
    {
      ((MyPanel1)siblings[0]).repaint();
    }
  }
}
public class CommonParent extends JFrame
{
  MyPanel1 p1;
  MyPanel2 p2;
  public CommonParent()
  {
    p1 = new MyPanel1();
    p1.setBackground( Color.red );
    p1.setPreferredSize( new Dimension( 100, 200 ) );
    p2 = new MyPanel2();
    p2.setBackground( Color.green );
    p2.setPreferredSize( new Dimension( 200, 200 ) );
    
    getContentPane().add( p1, "North" );
    getContentPane().add( p2, "South" );
    setSize( 500, 500 );
  }
  public static void main(String[] args) 
  {
    new CommonParent().setVisible( true );
  }
}

If you don't have a common parent, you will need to pass a reference to the first panel into the constructor of the second in order to have a handle on the component you want to paint into.

public class Panel2 extends JPanel
{
  Panel1 p1;
  public Panel2( Panel1 p1 ) 
  {
    this.p1 = p1;
  }
  public someMethod()
  {
    if( p1 != null )
    {
      p1.repaint();
    }
  }
}

Regards,
Manfred.

[Vinod Venugopal]

Thanx guys for the feedback, ..Manfred, mine is something similar to the commonparent types except that commonparent is a frame itself, also I just dont need to repaint, based on values obtained from some table based operation in p1 I have to drawrect in p2..& this is dynamic..that means the Graphics context object needs to be active all the time..
Just doing drawrect was creating problems so I tried with adding JLabels with borders & empty text so it looks like rectangles, works out somewhat ok, but it would be gr8 to use graphics object & tinker with drawRect.

[Vinod Venugopal]

Oops sorry , I would like to correct the message above, commponparent is a Panel like MyPanel...