* a section in <em>The Java Tutorial.</em>
 * <p>
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans<sup><font size="-2">TM</font></sup>
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @see Box
 * @see java.awt.ComponentOrientation
 * @see JComponent#getAlignmentX
 * @see JComponent#getAlignmentY
 *
 * @author   Timothy Prinzing
 * @version 1.37 04/10/06 
 */
public class BoxLayout implements LayoutManager2, Serializable {

    /**
     * Specifies that components should be laid out left to right.
     */
    public static final int X_AXIS = 0;
    
    /**
     * Specifies that components should be laid out top to bottom.
     */
    public static final int Y_AXIS = 1;

    /**
     * Specifies that components should be laid out in the direction of 
     * a line of text as determined by the target container's
     * <code>ComponentOrientation</code> property.  
     */
    public static final int LINE_AXIS = 2;

    /**
     * Specifies that components should be laid out in the direction that
     * lines flow across a page as determined by the target container's
     * <code>ComponentOrientation</code> property.
     */
    public static final int PAGE_AXIS = 3;

    /**
     * Creates a layout manager that will lay out components along the
     * given axis.  
     *
     * @param target  the container that needs to be laid out
     * @param axis  the axis to lay out components along. Can be one of:
     *              <code>BoxLayout.X_AXIS</code>,
     *              <code>BoxLayout.Y_AXIS</code>,
     *              <code>BoxLayout.LINE_AXIS</code> or
     *              <code>BoxLayout.PAGE_AXIS</code>
     *
     * @exception AWTError  if the value of <code>axis</code> is invalid 
     */
    public BoxLayout(Container target, int axis) {
        if (axis != X_AXIS && axis != Y_AXIS && 
            axis != LINE_AXIS && axis != PAGE_AXIS) {
            throw new AWTError("Invalid axis");
        }
        this.axis = axis;
        this.target = target;
    }

    /**
     * Constructs a BoxLayout that 
     * produces debugging messages.
     *
     * @param target  the container that needs to be laid out
     * @param axis  the axis to lay out components along. Can be one of:
     *              <code>BoxLayout.X_AXIS</code>,
     *              <code>BoxLayout.Y_AXIS</code>,
     *              <code>BoxLayout.LINE_AXIS</code> or
     *              <code>BoxLayout.PAGE_AXIS</code>
     *
     * @param dbg  the stream to which debugging messages should be sent,
     *   null if none
     */
    BoxLayout(Container target, int axis, PrintStream dbg) {
        this(target, axis);
        this.dbg = dbg;
    }

    /**
     * Returns the container that uses this layout manager.
     *
     * @return the container that uses this layout manager
     *
     * @since 1.6
     */
    public final Container getTarget() {
        return this.target;
    }

    /**
     * Returns the axis that was used to lay out components.
     * Returns one of: