Resizing Panels

Here is my code.I don't really know how to use Gridbag Layout. Why doesn't it work with setSize or setPreferredSize?

thx for any help.

import java.awt.Dimension;

import java.awt.GridLayout;

import javax.swing.BorderFactory;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JPanel;

public class threePanels{

JFrame frame;

JPanel panelLeft,panelCenter,panelRight,mainPanel;

JButton button1,button2,button3;

public threePanels(){

frame=new JFrame("3 panels in a frame");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

button1=new JButton("Left");

button2=new JButton("Center");

button3=new JButton("Right");

mainPanel=new JPanel(new GridLayout(1,0));

panelLeft=new JPanel();

panelLeft.setBorder(BorderFactory.createTitledBorder("1st panel"));

panelCenter=new JPanel();

panelCenter.setBorder(BorderFactory.createTitledBorder("2nd panel"));

panelRight=new JPanel();

panelRight.setBorder(BorderFactory.createTitledBorder("3rd panel"));

panelLeft.add(button1);

panelCenter.add(button2);

panelRight.add(button3);

/*

int width = 300;

panelLeft.setSize(width, 400);

panelCenter.setSize(width*2, 400);

panelRight.setSize(width/2, 400);

*/

int width = 100;

panelLeft.setPreferredSize(new Dimension(width,400));

panelCenter.setPreferredSize(new Dimension(width*2,400));

panelRight.setPreferredSize(new Dimension(width/2,400));

mainPanel.add(panelLeft);

mainPanel.add(panelCenter);

mainPanel.add(panelRight);

frame.add(mainPanel);

frame.pack();

frame.setVisible(true);

}

public static void main(String[] args){

javax.swing.SwingUtilities.invokeLater(new Runnable(){

public void run() {

threePanels start =new threePanels();

}

});

}

}

javahelpsa at 2007-7-15 4:58:14 >