How to Condense BoxLayout in Java

Question

I'm using a vertical BoxLayout for a panel that is nested in some other panels. The size of the other panels causes the objects in my target panel to spread out in an unsightly manner. How do I make the panel present the objects from top to bottom without so much padding?

The following is similar code, although it produces spinners that fill the entire panel instead of normal looking spinners placed very far apart.

 import java.awt.Dimension;
 import javax.swing.BoxLayout;
 import javax.swing.JFrame;
 import javax.swing.JLabel;
 import javax.swing.JPanel;
 import javax.swing.JSpinner;
 import javax.swing.SpinnerNumberModel;

 public class PanelTest {

  public static void main(String[] args){
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JPanel mainPanel = new JPanel();
    mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.X_AXIS));

    JPanel leftPanel = new JPanel();
    leftPanel.setLayout(new BoxLayout(leftPanel, BoxLayout.Y_AXIS));

    JPanel spinPanel1 = new JPanel();
    spinPanel1.setLayout(new BoxLayout(spinPanel1, BoxLayout.X_AXIS));
    spinPanel1.add(new JLabel("top"));
    SpinnerNumberModel spinMod1 = new SpinnerNumberModel(0,0,10,1);
    spinPanel1.add(new JSpinner(spinMod1));
    leftPanel.add(spinPanel1);

    JPanel spinPanel2 = new JPanel();
    spinPanel2.setLayout(new BoxLayout(spinPanel2, BoxLayout.X_AXIS));
    spinPanel2.add(new JLabel("bottom"));
    SpinnerNumberModel spinMod2 = new SpinnerNumberModel(0,0,10,1);
    spinPanel2.add(new JSpinner(spinMod2));
    leftPanel.add(spinPanel2);

    JPanel rightPanel = new JPanel();
    rightPanel.setPreferredSize(new Dimension(800,600));

    mainPanel.add(leftPanel);
    mainPanel.add(rightPanel);
    frame.getContentPane().add(mainPanel);
    frame.pack();
    frame.setVisible(true);
  }
 }

Answer 1

There are many ways to do this, mostly involving adding the panel with a (constraint /) layout that will honor the preferred size. In this case we use a GridBagLayout with default constraints. The component (leftPanel) added to it, is centered within the available space.

Each panel has a colored border to make its extent more obvious. This is a handy visual technique to use when debugging 'layout compaction'problems.

As an aside, I think the leftPanel looks crowded, and the non aligned spinners further detract from the appearance. I'd probably use a GridBagLayout for the labels and text fields (all in a single panel) with some padding & the labels right aligned.

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

public class PanelTest {

    public static void main(String[] args) {
        // any single component added to this will be centered & have
        // its preferred size honored.
        JPanel constrainSpinnerPanel = new JPanel(new GridBagLayout());
        constrainSpinnerPanel.setBorder(new LineBorder(Color.CYAN, 4));
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel mainPanel = new JPanel();
        mainPanel.setBorder(new LineBorder(Color.RED,4));
        mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.X_AXIS));

        JPanel leftPanel = new JPanel();
        leftPanel.setBorder(new LineBorder(Color.BLUE,4));
        leftPanel.setLayout(new BoxLayout(leftPanel, BoxLayout.Y_AXIS));

        JPanel spinPanel1 = new JPanel();
        spinPanel1.setLayout(new BoxLayout(spinPanel1, BoxLayout.X_AXIS));
        spinPanel1.add(new JLabel("top"));
        SpinnerNumberModel spinMod1 = new SpinnerNumberModel(0, 0, 10, 1);
        spinPanel1.add(new JSpinner(spinMod1));
        leftPanel.add(spinPanel1);

        JPanel spinPanel2 = new JPanel();
        spinPanel2.setLayout(new BoxLayout(spinPanel2, BoxLayout.X_AXIS));
        spinPanel2.add(new JLabel("bottom"));
        SpinnerNumberModel spinMod2 = new SpinnerNumberModel(0, 0, 10, 1);
        spinPanel2.add(new JSpinner(spinMod2));
        leftPanel.add(spinPanel2);

        JPanel rightPanel = new JPanel();
        rightPanel.setBorder(new LineBorder(Color.GREEN, 4));
        rightPanel.setPreferredSize(new Dimension(400, 100));

        constrainSpinnerPanel.add(leftPanel);
        mainPanel.add(constrainSpinnerPanel);
        //mainPanel.add(leftPanel);
        mainPanel.add(rightPanel);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setVisible(true);
    }
}