JPanel which layout

Question

Say I have a frame and I want to create 6 panels in it like so:

which layout would be the best? I tried something like this:

public static void main ( String[] args ) {
        JFrame frame = new JFrame("Testing");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(800,600));
        frame.setLayout(new FlowLayout(FlowLayout.LEFT));

        JPanel leftTop = new JPanel();
        leftTop.setPreferredSize(new Dimension(251,300));
        leftTop.setBackground(Color.black);
        frame.getContentPane().add(leftTop);

        JPanel middleTop = new JPanel();
        middleTop.setPreferredSize(new Dimension(251,300));
        middleTop.setBackground(Color.white);
        frame.getContentPane().add(middleTop);

        JPanel rightTop = new JPanel();
        rightTop.setPreferredSize(new Dimension(251,300));
        rightTop.setBackground(Color.red);
        frame.getContentPane().add(rightTop);

        JPanel leftBottom = new JPanel();
        leftBottom.setPreferredSize(new Dimension(251,300));
        leftBottom.setBackground(Color.green);
        frame.getContentPane().add(leftBottom);

        JPanel middleBottom = new JPanel();
        middleBottom.setPreferredSize(new Dimension(251,300));
        middleBottom.setBackground(Color.yellow);
        frame.getContentPane().add(middleBottom);

        JPanel rightBottom = new JPanel();
        rightBottom.setPreferredSize(new Dimension(251,300));
        rightBottom.setBackground(Color.black);
        frame.getContentPane().add(rightBottom);

        frame.pack();
        frame.setVisible(true);
    }

but if I change the size of a panel it will not turn out so nice haha.

Answer 1

Say you have a JFrame, and you want 6 JPanels in it like so:

The way to create this GUI is to divide and conquer.

1. You must start a Swing application with a call to the SwingUtilities invokeLater method, to put the creation and execution of the Swing components on the Event Dispatch thread. Yes, even for small testing programs.

2. I created 3 JPanels for the left, center, and right. Each of these JPanels uses a BorderLayout.

3. Yes, I had to specify a preferred size for the 6 inner JPanels. This is because the 6 inner JPanels don't have any internal Swing components. Generally in Swing, you should let Swing components size themselves.

4. I enclosed the left, center, and right JPanels in a main JPanel. Generally, you should not add any Swing components to a JFrame, other than JPanel and JScrollPane. Unexplanable bad things happen when you violate this rule. I'd rather find and fix my own coding mistakes than to use Java classes in an unusual way.

Here's the code.

package com.ggl.testing;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class LayoutTest implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new LayoutTest());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame("Layout Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel mainPanel = new JPanel();
        mainPanel.add(createLeftPanel());
        mainPanel.add(createCenterPanel());
        mainPanel.add(createRightPanel());

        frame.add(mainPanel);

        frame.pack();
        frame.setVisible(true);
    }

    private JPanel createLeftPanel() {
        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());

        JPanel leftTop = new JPanel();
        leftTop.setPreferredSize(new Dimension(251, 250));
        leftTop.setBackground(Color.black);
        panel.add(leftTop, BorderLayout.NORTH);

        JPanel leftBottom = new JPanel();
        leftBottom.setPreferredSize(new Dimension(251, 350));
        leftBottom.setBackground(Color.green);
        panel.add(leftBottom, BorderLayout.SOUTH);

        return panel;
    }

    private JPanel createCenterPanel() {
        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());

        JPanel middleTop = new JPanel();
        middleTop.setPreferredSize(new Dimension(251, 400));
        middleTop.setBackground(Color.cyan);
        panel.add(middleTop, BorderLayout.NORTH);

        JPanel middleBottom = new JPanel();
        middleBottom.setPreferredSize(new Dimension(251, 200));
        middleBottom.setBackground(Color.yellow);
        panel.add(middleBottom, BorderLayout.SOUTH);

        return panel;
    }

    private JPanel createRightPanel() {
        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());

        JPanel rightTop = new JPanel();
        rightTop.setPreferredSize(new Dimension(251, 100));
        rightTop.setBackground(Color.red);
        panel.add(rightTop, BorderLayout.NORTH);

        JPanel rightBottom = new JPanel();
        rightBottom.setPreferredSize(new Dimension(251, 500));
        rightBottom.setBackground(Color.black);
        panel.add(rightBottom, BorderLayout.SOUTH);

        return panel;
    }

}