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

If you are having only one panel in frame and nothing else then try this:

• Set BorderLayout in frame.
• Add panel in frame with BorderLayout.CENTER

---

May be this is happening because of while loop in JPanel.(Not sure why? finding actual reason. Will update when find it.) If you replace it with paintComponent(g) method all works fine:

public BSTest() {
    //--- your code as it is
    add(panel, BorderLayout.CENTER);
    //-- removed panel.drawStuff();
}

public class DrawPanel extends JPanel {
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.BLACK);
        System.out.println("W:" + getSize().width + ", H:" + getSize().height);
        g2d.fillRect(0, 0, getSize().width, getSize().height);
    }
 }

//your code as it is.