ColumnLayout : Customized Layout « Swing JFC « Java


 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit

import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import java.awt.Insets;
import java.awt.LayoutManager2;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

 * This LayoutManager arranges the components into a column. Components are
 * always given their preferred size.
 * When you create a ColumnLayout, you may specify four values: margin_height --
 * how much space to leave on top and bottom margin_width -- how much space to
 * leave on left and right spacing -- how much vertical space to leave between
 * items alignment -- the horizontal position of the components:
 * ColumnLayout.LEFT -- left-justify the components ColumnLayout.CENTER --
 * horizontally center the components ColumnLayout.RIGHT -- right-justify the
 * components
 * You never call the methods of a ColumnLayout object. Just create one and make
 * it the layout manager for your container by passing it to the addLayout()
 * method of the Container object.
public class ColumnLayout implements LayoutManager2 {
  protected int margin_height;

  protected int margin_width;

  protected int spacing;

  protected int alignment;

  // Constants for the alignment argument to the constructor.
  public static final int LEFT = 0;

  public static final int CENTER = 1;

  public static final int RIGHT = 2;

  /** The constructor. See comment above for meanings of these arguments */
  public ColumnLayout(int margin_height, int margin_width, int spacing,
      int alignment) {
    this.margin_height = margin_height;
    this.margin_width = margin_width;
    this.spacing = spacing;
    this.alignment = alignment;

   * A default constructor that creates a ColumnLayout using 5-pixel margin
   * width and height, 5-pixel spacing, and left alignment
  public ColumnLayout() {
    this(5, 5, 5, LEFT);

   * The method that actually performs the layout. Called by the Container
  public void layoutContainer(Container parent) {
    Insets insets = parent.getInsets();
    Dimension parent_size = parent.getSize();
    Component kid;
    int nkids = parent.getComponentCount();
    int x0 = insets.left + margin_width; // The base X position
    int x;
    int y = + margin_height; // Start at the top of the column

    for (int i = 0; i < nkids; i++) { // Loop through the kids
      kid = parent.getComponent(i); // Get the kid
      if (!kid.isVisible())
        continue; // Skip hidden ones
      Dimension pref = kid.getPreferredSize(); // How big is it?
      switch (alignment) { // Compute X coordinate
      case LEFT:
        x = x0;
      case CENTER:
        x = (parent_size.width - pref.width) / 2;
      case RIGHT:
        x = parent_size.width - insets.right - margin_width
            - pref.width;
      // Set the size and position of this kid
      kid.setBounds(x, y, pref.width, pref.height);
      y += pref.height + spacing; // Get Y position of the next one

  /** The Container calls this to find out how big the layout should to be */
  public Dimension preferredLayoutSize(Container parent) {
    return layoutSize(parent, 1);

  /** The Container calls this to find out how big the layout must be */
  public Dimension minimumLayoutSize(Container parent) {
    return layoutSize(parent, 2);

  /** The Container calls this to find out how big the layout can be */
  public Dimension maximumLayoutSize(Container parent) {
    return layoutSize(parent, 3);

  // Compute min, max, or preferred size of all the visible children
  protected Dimension layoutSize(Container parent, int sizetype) {
    int nkids = parent.getComponentCount();
    Dimension size = new Dimension(0, 0);
    Insets insets = parent.getInsets();
    int num_visible_kids = 0;

    // Compute maximum width and total height of all visible kids
    for (int i = 0; i < nkids; i++) {
      Component kid = parent.getComponent(i);
      Dimension d;
      if (!kid.isVisible())
      if (sizetype == 1)
        d = kid.getPreferredSize();
      else if (sizetype == 2)
        d = kid.getMinimumSize();
        d = kid.getMaximumSize();
      if (d.width > size.width)
        size.width = d.width;
      size.height += d.height;

    // Now add in margins and stuff
    size.width += insets.left + insets.right + 2 * margin_width;
    size.height += + insets.bottom + 2 * margin_height;
    if (num_visible_kids > 1)
      size.height += (num_visible_kids - 1) * spacing;
    return size;

  // Other LayoutManager(2) methods that are unused by this class
  public void addLayoutComponent(String constraint, Component comp) {

  public void addLayoutComponent(Component comp, Object constraint) {

  public void removeLayoutComponent(Component comp) {

  public void invalidateLayout(Container parent) {

  public float getLayoutAlignmentX(Container parent) {
    return 0.5f;

  public float getLayoutAlignmentY(Container parent) {
    return 0.5f;

class ColumnLayoutPane extends JPanel {
  public ColumnLayoutPane() {
    // Get rid of the default layout manager.
    // We'll arrange the components ourselves.
    this.setLayout(new ColumnLayout(5, 5, 10, ColumnLayout.RIGHT));

    // Create some buttons and set their sizes and positions explicitly
    for (int i = 0; i < 6; i++) {
      int pointsize = 8 + i * 2;
      JButton b = new JButton("Point size " + pointsize);
      b.setFont(new Font("helvetica", Font.BOLD, pointsize));
  public static void main(String[] a) {
    JFrame f = new JFrame();
    f.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {

    f.setContentPane(new ColumnLayoutPane());



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