Question

I made a JComponent that displays a rectangle of a specified color. (Haven’t found any other way to achieve this effect). Problem is, it doesn’t follow JFrame.pack() and Layout Managers as expected.

Code:

import java.awt.*;
import javax.swing.*;

public class FooRunnable implements Runnable{

private class ColorSample extends JComponent{

    private Color sampleColor;
    private int width, height;

    public ColorSample(int rgb, int w, int h){
        sampleColor = new Color(rgb);
        width = w;
        height = h;
    }

    public Dimension getSize(){
        return new Dimension(width, height);
    }

    public int getWidth(){
        return width;
    }

    public int getHeight(){
        return height;
    }

    public boolean isDisplayable(){
        return true;
    }

    public void paintComponent(Graphics g){
        g.setColor(sampleColor);
        g.fillRect(0, 0, width, height);
    }

}

public void run(){
    JFrame mainFrame = new JFrame();
    //mainFrame.setSize(500, 300);
    Container mainContent = mainFrame.getContentPane();
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    mainContent.setLayout(new BoxLayout(mainContent, BoxLayout.PAGE_AXIS));

    JPanel specifyFilePanel = new JPanel();
    specifyFilePanel.setLayout(new BoxLayout(specifyFilePanel, BoxLayout.LINE_AXIS));
    JLabel filenameLabel = new JLabel("File:       ");
    JButton browseButton = new JButton("Browse...");
    specifyFilePanel.add(Box.createHorizontalStrut(8));
    specifyFilePanel.add(filenameLabel);
    specifyFilePanel.add(browseButton);
    specifyFilePanel.add(Box.createHorizontalStrut(8));

    JPanel colorStatusPanel = new JPanel();
    colorStatusPanel.setLayout(new BoxLayout(colorStatusPanel, BoxLayout.Y_AXIS));
    JLabel statusLabel = new JLabel("");
    JButton roll = new JButton("Operate");
    colorStatusPanel.add(new ColorSample(Color.red.getRGB(), 50, 100));
    colorStatusPanel.add(statusLabel);
    colorStatusPanel.add(roll);

    mainContent.add(Box.createVerticalStrut(5));
    mainContent.add(specifyFilePanel);
    mainContent.add(Box.createVerticalStrut(10));
    mainContent.add(colorStatusPanel);
    mainContent.add(new JPanel());
    mainFrame.pack();
    mainFrame.setVisible(true);
}

}

I tried experimenting between pack and explicitly specifying the frame’s size. Here are the default appearances of my GUI on various settings:

Plain mainFrame.pack():

mainFrame.setSize(500, 500):

mainFrame.setSize(500, 300):

The closest to what I intend to achieve is mainFrame.setSize(500, 500) although, as I plan to add a few more components, I expect it will be fragile. As you see, in the other two, the “Operate” button overlaps with the ColorSample Component—like it’s not following the Layout Manager I set. And then see how pack cuts of the ColorSample Component. Any tips on how I can achieve the effect I want?

Answer 1

LayoutManagers are free to size/position components as they deem appropriate, components cannot force them but only give hints in their getXXSize (XX == min/pref/max) methods. So the best a component implementation can do is

• implement all getXXSize and return the size they ideally want
• implement paintComponent to cope with a differing size

a snippet only

public class MyBox extends JComponent {
     Dimension boxSize;

     public void setBoxSize(Dimension box) {
         this.boxSize = new Dimension(box);
         ...   
     } 

     @Override
     public void paintComponent(Graphics g) {
         super.paintComponent(g);
         // position the box in the actual size
         // and paint it 
     }

     @Override
     public Dimension getPreferredSize() {
         return getBoxSize();
     }
     @Override // same for min/max
     public Dimension getM...Size( {
         return getBoxSize();
     }
}