Java - JPanel is only one small pixel in the top center of my JFrame

Question

The JPanel called panel only shows up as one small red square up the top center, I have tried to set the size but it doesn't seem to do anything.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JFrame;
import javax.swing.JPanel;   

public class Draw extends JFrame{

private JPanel panel;

    public Draw() {
        super("title");
        setLayout(new FlowLayout());        
        panel = new JPanel();       
        panel.setBackground(Color.RED);
        add(panel, BorderLayout.CENTER);
    }
}

MadProgrammer · Accepted Answer · 2013-11-08T08:51:20.027

5

The default, preferred size of a JPanel is 0x0. FlowLayout lays out components based on their preferred size, hence the component now has a preferred size of 1x1 (the line border adds a little weight).

You could try adding another component to panel...

panel.add(new JLabel("This is some text"));

Or override panels getPreferredSize method...

panel = new JPanel() {
    public Dimension getPreferredSize() {
        return new Dimension(100, 100);
    }
};

edited Nov 08 '13 at 08:51

answered Nov 08 '13 at 08:42

MadProgrammer

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quick answer +1,I always see you answering in swing.Looks like you have some 10-15 years of exp in this field – SpringLearner Nov 08 '13 at 08:44
@javaBeginner Being coding Swing just after it was introduced into the core API in Swing 1.3 (around 1999). Still lots to learn though ;) – MadProgrammer Nov 08 '13 at 08:46
Any experience in javaFX? – SpringLearner Nov 08 '13 at 08:49
@javaBeginner Not as yet. I wasn't that interested until they got a table and tree component ;) – MadProgrammer Nov 08 '13 at 08:49
1

Thank you so much. I didn't quite realise how `FlowLayout` worked, so I took that out and it worked fine. Their* btw :P – Aazim Abdul Nov 08 '13 at 08:50
@MadProgrammer another question waiting for you http://stackoverflow.com/questions/19854885/how-to-resize-horizontal-jtree-java-swing-by-mouse-when-application-is-running – SpringLearner Nov 08 '13 at 08:50
@IsaacGuethert Please accpet answers if it solves your problem.I see people saying thanks,it solved but does not accept answers.I feel ashamed asking to accept my answer.But have this habit of accepting answers – SpringLearner Nov 08 '13 at 08:52
@javaBeginner There is a 7 minute countdown before I can accept answers.I can assure you I did have my finger on the button. – Aazim Abdul Nov 08 '13 at 08:57
@IsaacGuethert It's always nice to see if another answer comes along ;) – MadProgrammer Nov 08 '13 at 09:06

score 1 · Answer 2 · edited Nov 08 '13 at 10:52

Try this :

File Draw.java

   package com.stackovfl;

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

    @SuppressWarnings("serial")
    class Draw extends JFrame {
    private JPanel panel;

      public Draw() {
        super("title");
        setLayout(new FlowLayout());
        panel = new JPanel();
        panel.setPreferredSize(new Dimension(200, 300));
        panel.setBackground(Color.RED);     
        add(panel, BorderLayout.CENTER);
        /* Important to get the layout to work */
        pack();     
        /* Center the window */
        setLocationRelativeTo(null);        
        /* Important if you want to see your window :) */
        setVisible(true);
        }
    }

File Test.java (main method to launch the window) : package com.stackovfl;

import javax.swing.SwingUtilities;

public class Test {
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new Draw();
        }
    });
   }
}

Note that it is important to use the setLocationRelativeTo(null) after the pack() method. This ensures that your windows is at the center of your screen. If you try it the other way around it will not work because the pack method can modify the size of your window. — a_mid, Nov 10 '13 at 19:57

Java - JPanel is only one small pixel in the top center of my JFrame

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