How to make a JPanel inside a JFrame fill the whole window?

Question

In the below example, how can I get the JPanel to take up all of the JFrame? I set the preferred size to 800x420 but it only actually fills 792x391.

import j         


        

Answer 1

Here's an alternative using pack instead.

import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PackExample extends JFrame {

    public PackExample(){
        JPanel panel = new JPanel();
        panel.setPreferredSize(new Dimension(800,600));
        panel.setBackground(Color.green);
        add(panel);
        pack();
        setVisible(true);
   }

   public static void main(String[] args){
     new PackExample();
   }

}