https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package javax.swing;

import java.awt.*;
import java.beans.ConstructorProperties;
import java.io.Serializable;
import java.io.PrintStream;


A layout manager that allows multiple components to be laid out either
vertically or horizontally. The components will not wrap so, for
example, a vertical arrangement of components will stay vertically
arranged when the frame is resized.


  
Example:
  





Nesting multiple panels with different combinations of horizontal and
vertical gives an effect similar to GridBagLayout, without the
complexity. The diagram shows two panels arranged horizontally, each
of which contains 3 components arranged vertically.

 The BoxLayout manager is constructed with an axis parameter that
specifies the type of layout that will be done. There are four choices:

X_AXIS - Components are laid out horizontally
from left to right.


Y_AXIS - Components are laid out vertically
from top to bottom.


LINE_AXIS - Components are laid out the way words are laid out in a line, based on the container's ComponentOrientation property. If the container's ComponentOrientation is horizontal then components are laid out horizontally, otherwise they are laid out vertically. For horizontal orientations, if the container's ComponentOrientation is left to right then components are laid out left to right, otherwise they are laid out right to left. For vertical orientations components are always laid out from top to bottom.


PAGE_AXIS - Components are laid out the way text lines are laid out on a page, based on the container's ComponentOrientation property. If the container's ComponentOrientation is horizontal then components are laid out vertically, otherwise they are laid out horizontally. For horizontal orientations, if the container's ComponentOrientation is left to right then components are laid out left to right, otherwise they are laid out right to left. For vertical orientations components are always laid out from top to bottom.



For all directions, components are arranged in the same order as they were
added to the container.


BoxLayout attempts to arrange components
at their preferred widths (for horizontal layout)
or heights (for vertical layout).
For a horizontal layout,
if not all the components are the same height,
BoxLayout attempts to make all the components
as high as the highest component.
If that's not possible for a particular component,
then BoxLayout aligns that component vertically,
according to the component's Y alignment.
By default, a component has a Y alignment of 0.5,
which means that the vertical center of the component
should have the same Y coordinate as
the vertical centers of other components with 0.5 Y alignment.

 Similarly, for a vertical layout, BoxLayout attempts to make all components in the column as wide as the widest component. If that fails, it aligns them horizontally according to their X alignments. For PAGE_AXIS layout, horizontal alignment is done based on the leading edge of the component. In other words, an X alignment value of 0.0 means the left edge of a component if the container's ComponentOrientation is left to right and it means the right edge of the component otherwise. 

Instead of using BoxLayout directly, many programs use the Box class.
The Box class is a lightweight container that uses a BoxLayout.
It also provides handy methods to help you use BoxLayout well.
Adding components to multiple nested boxes is a powerful way to get
the arrangement you want.


For further information and examples see
How to Use BoxLayout,
a section in The Java Tutorial.


Warning: 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 has been added to the java.beans package. Please see XMLEncoder. 
Author:  Timothy Prinzing
See Also:
Since:1.2
/**
 * A layout manager that allows multiple components to be laid out either
 * vertically or horizontally. The components will not wrap so, for
 * example, a vertical arrangement of components will stay vertically
 * arranged when the frame is resized.
 * <div style="float:right;text-align:center">
 *   <p><b>Example:</b>
 *   <p><img src="doc-files/BoxLayout-1.gif"
 *      alt="The following text describes this graphic."
 *      width="191" height="201">
 * </div>
 * <p>
 * Nesting multiple panels with different combinations of horizontal and
 * vertical gives an effect similar to GridBagLayout, without the
 * complexity. The diagram shows two panels arranged horizontally, each
 * of which contains 3 components arranged vertically.
 *
 * <p> The BoxLayout manager is constructed with an axis parameter that
 * specifies the type of layout that will be done. There are four choices:
 *
 * <blockquote><b>{@code X_AXIS}</b> - Components are laid out horizontally
 * from left to right.</blockquote>
 *
 * <blockquote><b>{@code Y_AXIS}</b> - Components are laid out vertically
 * from top to bottom.</blockquote>
 *
 * <blockquote><b>{@code LINE_AXIS}</b> - Components are laid out the way
 * words are laid out in a line, based on the container's
 * {@code ComponentOrientation} property. If the container's
 * {@code ComponentOrientation} is horizontal then components are laid out
 * horizontally, otherwise they are laid out vertically.  For horizontal
 * orientations, if the container's {@code ComponentOrientation} is left to
 * right then components are laid out left to right, otherwise they are laid
 * out right to left. For vertical orientations components are always laid out
 * from top to bottom.</blockquote>
 *
 * <blockquote><b>{@code PAGE_AXIS}</b> - Components are laid out the way
 * text lines are laid out on a page, based on the container's
 * {@code ComponentOrientation} property. If the container's
 * {@code ComponentOrientation} is horizontal then components are laid out
 * vertically, otherwise they are laid out horizontally.  For horizontal
 * orientations, if the container's {@code ComponentOrientation} is left to
 * right then components are laid out left to right, otherwise they are laid
 * out right to left.&nbsp; For vertical orientations components are always
 * laid out from top to bottom.</blockquote>
 * <p>
 * For all directions, components are arranged in the same order as they were
 * added to the container.
 * <p>
 * BoxLayout attempts to arrange components
 * at their preferred widths (for horizontal layout)
 * or heights (for vertical layout).
 * For a horizontal layout,
 * if not all the components are the same height,
 * BoxLayout attempts to make all the components
 * as high as the highest component.
 * If that's not possible for a particular component,
 * then BoxLayout aligns that component vertically,
 * according to the component's Y alignment.
 * By default, a component has a Y alignment of 0.5,
 * which means that the vertical center of the component
 * should have the same Y coordinate as
 * the vertical centers of other components with 0.5 Y alignment.
 * <p>
 * Similarly, for a vertical layout,
 * BoxLayout attempts to make all components in the column
 * as wide as the widest component.
 * If that fails, it aligns them horizontally
 * according to their X alignments.  For {@code PAGE_AXIS} layout,
 * horizontal alignment is done based on the leading edge of the component.
 * In other words, an X alignment value of 0.0 means the left edge of a
 * component if the container's {@code ComponentOrientation} is left to
 * right and it means the right edge of the component otherwise.
 * <p>
 * Instead of using BoxLayout directly, many programs use the Box class.
 * The Box class is a lightweight container that uses a BoxLayout.
 * It also provides handy methods to help you use BoxLayout well.
 * Adding components to multiple nested boxes is a powerful way to get
 * the arrangement you want.
 * <p>
 * For further information and examples see
 * <a
 href="https://docs.oracle.com/javase/tutorial/uiswing/layout/box.html">How to Use BoxLayout</a>,
 * 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
 * has been added to the {@code java.beans} package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @see Box
 * @see java.awt.ComponentOrientation
 * @see JComponent#getAlignmentX
 * @see JComponent#getAlignmentY
 *
 * @author   Timothy Prinzing
 * @since 1.2
 */
@SuppressWarnings("serial")
public class BoxLayout implements LayoutManager2, Serializable {

    
Specifies that components should be laid out left to right.

/**
     * 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.

/**
     * 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 ComponentOrientation property. 
/**
     * Specifies that components should be laid out in the direction of
     * a line of text as determined by the target container's
     * {@code ComponentOrientation} 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 ComponentOrientation property. 
/**
     * 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} property.
     */
    public static final int PAGE_AXIS = 3;

    
Creates a layout manager that will lay out components along the
given axis.

Params:
  • target –  the container that needs to be laid out
  • axis –  the axis to lay out components along. Can be one of: BoxLayout.X_AXIS, BoxLayout.Y_AXIS,
             BoxLayout.LINE_AXIS or BoxLayout.PAGE_AXIS
Throws:
  • AWTError –  if the value of axis is invalid
/**
     * 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, BoxLayout.Y_AXIS,
     *              BoxLayout.LINE_AXIS} or {@code BoxLayout.PAGE_AXIS}
     *
     * @exception AWTError  if the value of {@code axis} is invalid
     */
    @ConstructorProperties({"target", "axis"})
    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.

Params:
  • target –  the container that needs to be laid out
  • axis –  the axis to lay out components along. Can be one of: BoxLayout.X_AXIS, BoxLayout.Y_AXIS,
             BoxLayout.LINE_AXIS or BoxLayout.PAGE_AXIS
  • dbg –  the stream to which debugging messages should be sent,
  null if none
/**
     * 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, BoxLayout.Y_AXIS,
     *              BoxLayout.LINE_AXIS} or {@code BoxLayout.PAGE_AXIS}
     *
     * @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.

Returns:the container that uses this layout manager
Since:1.6
/**
     * 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: BoxLayout.X_AXIS, BoxLayout.Y_AXIS,
BoxLayout.LINE_AXIS or BoxLayout.PAGE_AXIS 
Returns:the axis that was used to lay out components
Since:1.6
/**
     * Returns the axis that was used to lay out components.
     * Returns one of:
     * {@code BoxLayout.X_AXIS, BoxLayout.Y_AXIS,
     * BoxLayout.LINE_AXIS} or {@code BoxLayout.PAGE_AXIS}
     *
     * @return the axis that was used to lay out components
     *
     * @since 1.6
     */
    public final int getAxis() {
        return this.axis;
    }

    
Indicates that a child has changed its layout related information,
and thus any cached calculations should be flushed.


This method is called by AWT when the invalidate method is called
on the Container.  Since the invalidate method may be called
asynchronously to the event thread, this method may be called
asynchronously.

Params:
  • target –  the affected container
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
/**
     * Indicates that a child has changed its layout related information,
     * and thus any cached calculations should be flushed.
     * <p>
     * This method is called by AWT when the invalidate method is called
     * on the Container.  Since the invalidate method may be called
     * asynchronously to the event thread, this method may be called
     * asynchronously.
     *
     * @param target  the affected container
     *
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     */
    public synchronized void invalidateLayout(Container target) {
        checkContainer(target);
        xChildren = null;
        yChildren = null;
        xTotal = null;
        yTotal = null;
    }

    
Not used by this class.

Params:
  • name – the name of the component
  • comp – the component
/**
     * Not used by this class.
     *
     * @param name the name of the component
     * @param comp the component
     */
    public void addLayoutComponent(String name, Component comp) {
        invalidateLayout(comp.getParent());
    }

    
Not used by this class.

Params:
  • comp – the component
/**
     * Not used by this class.
     *
     * @param comp the component
     */
    public void removeLayoutComponent(Component comp) {
        invalidateLayout(comp.getParent());
    }

    
Not used by this class.

Params:
  • comp – the component
  • constraints – constraints
/**
     * Not used by this class.
     *
     * @param comp the component
     * @param constraints constraints
     */
    public void addLayoutComponent(Component comp, Object constraints) {
        invalidateLayout(comp.getParent());
    }

    
Returns the preferred dimensions for this layout, given the components
in the specified target container.

Params:
  • target –  the container that needs to be laid out
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
See Also:
Returns:the dimensions >= 0 && <= Integer.MAX_VALUE
/**
     * Returns the preferred dimensions for this layout, given the components
     * in the specified target container.
     *
     * @param target  the container that needs to be laid out
     * @return the dimensions &gt;= 0 &amp;&amp; &lt;= Integer.MAX_VALUE
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     * @see Container
     * @see #minimumLayoutSize
     * @see #maximumLayoutSize
     */
    public Dimension preferredLayoutSize(Container target) {
        Dimension size;
        synchronized(this) {
            checkContainer(target);
            checkRequests();
            size = new Dimension(xTotal.preferred, yTotal.preferred);
        }

        Insets insets = target.getInsets();
        size.width = (int) Math.min((long) size.width + (long) insets.left + (long) insets.right, Integer.MAX_VALUE);
        size.height = (int) Math.min((long) size.height + (long) insets.top + (long) insets.bottom, Integer.MAX_VALUE);
        return size;
    }

    
Returns the minimum dimensions needed to lay out the components
contained in the specified target container.

Params:
  • target –  the container that needs to be laid out
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
See Also:
Returns:the dimensions >= 0 && <= Integer.MAX_VALUE
/**
     * Returns the minimum dimensions needed to lay out the components
     * contained in the specified target container.
     *
     * @param target  the container that needs to be laid out
     * @return the dimensions &gt;= 0 &amp;&amp; &lt;= Integer.MAX_VALUE
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     * @see #preferredLayoutSize
     * @see #maximumLayoutSize
     */
    public Dimension minimumLayoutSize(Container target) {
        Dimension size;
        synchronized(this) {
            checkContainer(target);
            checkRequests();
            size = new Dimension(xTotal.minimum, yTotal.minimum);
        }

        Insets insets = target.getInsets();
        size.width = (int) Math.min((long) size.width + (long) insets.left + (long) insets.right, Integer.MAX_VALUE);
        size.height = (int) Math.min((long) size.height + (long) insets.top + (long) insets.bottom, Integer.MAX_VALUE);
        return size;
    }

    
Returns the maximum dimensions the target container can use
to lay out the components it contains.

Params:
  • target –  the container that needs to be laid out
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
See Also:
Returns:the dimensions >= 0 && <= Integer.MAX_VALUE
/**
     * Returns the maximum dimensions the target container can use
     * to lay out the components it contains.
     *
     * @param target  the container that needs to be laid out
     * @return the dimensions &gt;= 0 &amp;&amp; &lt;= Integer.MAX_VALUE
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     * @see #preferredLayoutSize
     * @see #minimumLayoutSize
     */
    public Dimension maximumLayoutSize(Container target) {
        Dimension size;
        synchronized(this) {
            checkContainer(target);
            checkRequests();
            size = new Dimension(xTotal.maximum, yTotal.maximum);
        }

        Insets insets = target.getInsets();
        size.width = (int) Math.min((long) size.width + (long) insets.left + (long) insets.right, Integer.MAX_VALUE);
        size.height = (int) Math.min((long) size.height + (long) insets.top + (long) insets.bottom, Integer.MAX_VALUE);
        return size;
    }

    
Returns the alignment along the X axis for the container.
If the box is horizontal, the default
alignment will be returned. Otherwise, the alignment needed
to place the children along the X axis will be returned.

Params:
  • target –  the container
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
Returns:the alignment >= 0.0f && <= 1.0f
/**
     * Returns the alignment along the X axis for the container.
     * If the box is horizontal, the default
     * alignment will be returned. Otherwise, the alignment needed
     * to place the children along the X axis will be returned.
     *
     * @param target  the container
     * @return the alignment &gt;= 0.0f &amp;&amp; &lt;= 1.0f
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     */
    public synchronized float getLayoutAlignmentX(Container target) {
        checkContainer(target);
        checkRequests();
        return xTotal.alignment;
    }

    
Returns the alignment along the Y axis for the container.
If the box is vertical, the default
alignment will be returned. Otherwise, the alignment needed
to place the children along the Y axis will be returned.

Params:
  • target –  the container
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
Returns:the alignment >= 0.0f && <= 1.0f
/**
     * Returns the alignment along the Y axis for the container.
     * If the box is vertical, the default
     * alignment will be returned. Otherwise, the alignment needed
     * to place the children along the Y axis will be returned.
     *
     * @param target  the container
     * @return the alignment &gt;= 0.0f &amp;&amp; &lt;= 1.0f
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     */
    public synchronized float getLayoutAlignmentY(Container target) {
        checkContainer(target);
        checkRequests();
        return yTotal.alignment;
    }

    
Called by the AWT  when the specified container
needs to be laid out.

Params:
  • target –  the container to lay out
Throws:
  • AWTError –  if the target isn't the container specified to the
                     BoxLayout constructor
/**
     * Called by the AWT <!-- XXX CHECK! --> when the specified container
     * needs to be laid out.
     *
     * @param target  the container to lay out
     *
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     */
    public void layoutContainer(Container target) {
        checkContainer(target);
        int nChildren = target.getComponentCount();
        int[] xOffsets = new int[nChildren];
        int[] xSpans = new int[nChildren];
        int[] yOffsets = new int[nChildren];
        int[] ySpans = new int[nChildren];

        Dimension alloc = target.getSize();
        Insets in = target.getInsets();
        alloc.width -= in.left + in.right;
        alloc.height -= in.top + in.bottom;

        // Resolve axis to an absolute value (either X_AXIS or Y_AXIS)
        ComponentOrientation o = target.getComponentOrientation();
        int absoluteAxis = resolveAxis( axis, o );
        boolean ltr = (absoluteAxis != axis) ? o.isLeftToRight() : true;


        // determine the child placements
        synchronized(this) {
            checkRequests();

            if (absoluteAxis == X_AXIS) {
                SizeRequirements.calculateTiledPositions(alloc.width, xTotal,
                                                         xChildren, xOffsets,
                                                         xSpans, ltr);
                SizeRequirements.calculateAlignedPositions(alloc.height, yTotal,
                                                           yChildren, yOffsets,
                                                           ySpans);
            } else {
                SizeRequirements.calculateAlignedPositions(alloc.width, xTotal,
                                                           xChildren, xOffsets,
                                                           xSpans, ltr);
                SizeRequirements.calculateTiledPositions(alloc.height, yTotal,
                                                         yChildren, yOffsets,
                                                         ySpans);
            }
        }

        // flush changes to the container
        for (int i = 0; i < nChildren; i++) {
            Component c = target.getComponent(i);
            c.setBounds((int) Math.min((long) in.left + (long) xOffsets[i], Integer.MAX_VALUE),
                        (int) Math.min((long) in.top + (long) yOffsets[i], Integer.MAX_VALUE),
                        xSpans[i], ySpans[i]);

        }
        if (dbg != null) {
            for (int i = 0; i < nChildren; i++) {
                Component c = target.getComponent(i);
                dbg.println(c.toString());
                dbg.println("X: " + xChildren[i]);
                dbg.println("Y: " + yChildren[i]);
            }
        }

    }

    void checkContainer(Container target) {
        if (this.target != target) {
            throw new AWTError("BoxLayout can't be shared");
        }
    }

    void checkRequests() {
        if (xChildren == null || yChildren == null) {
            // The requests have been invalidated... recalculate
            // the request information.
            int n = target.getComponentCount();
            xChildren = new SizeRequirements[n];
            yChildren = new SizeRequirements[n];
            for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (!c.isVisible()) {
                    xChildren[i] = new SizeRequirements(0,0,0, c.getAlignmentX());
                    yChildren[i] = new SizeRequirements(0,0,0, c.getAlignmentY());
                    continue;
                }
                Dimension min = c.getMinimumSize();
                Dimension typ = c.getPreferredSize();
                Dimension max = c.getMaximumSize();
                xChildren[i] = new SizeRequirements(min.width, typ.width,
                                                    max.width,
                                                    c.getAlignmentX());
                yChildren[i] = new SizeRequirements(min.height, typ.height,
                                                    max.height,
                                                    c.getAlignmentY());
            }

            // Resolve axis to an absolute value (either X_AXIS or Y_AXIS)
            int absoluteAxis = resolveAxis(axis,target.getComponentOrientation());

            if (absoluteAxis == X_AXIS) {
                xTotal = SizeRequirements.getTiledSizeRequirements(xChildren);
                yTotal = SizeRequirements.getAlignedSizeRequirements(yChildren);
            } else {
                xTotal = SizeRequirements.getAlignedSizeRequirements(xChildren);
                yTotal = SizeRequirements.getTiledSizeRequirements(yChildren);
            }
        }
    }

    
Given one of the 4 axis values, resolve it to an absolute axis.
The relative axis values, PAGE_AXIS and LINE_AXIS are converted
to their absolute couterpart given the target's ComponentOrientation
value.  The absolute axes, X_AXIS and Y_AXIS are returned unmodified.

Params:
  • axis – the axis to resolve
  • o – the ComponentOrientation to resolve against
Returns:the resolved axis
/**
     * Given one of the 4 axis values, resolve it to an absolute axis.
     * The relative axis values, PAGE_AXIS and LINE_AXIS are converted
     * to their absolute couterpart given the target's ComponentOrientation
     * value.  The absolute axes, X_AXIS and Y_AXIS are returned unmodified.
     *
     * @param axis the axis to resolve
     * @param o the ComponentOrientation to resolve against
     * @return the resolved axis
     */
    private int resolveAxis( int axis, ComponentOrientation o ) {
        int absoluteAxis;
        if( axis == LINE_AXIS ) {
            absoluteAxis = o.isHorizontal() ? X_AXIS : Y_AXIS;
        } else if( axis == PAGE_AXIS ) {
            absoluteAxis = o.isHorizontal() ? Y_AXIS : X_AXIS;
        } else {
            absoluteAxis = axis;
        }
        return absoluteAxis;
   }


    private int axis;
    private Container target;

    private transient SizeRequirements[] xChildren;
    private transient SizeRequirements[] yChildren;
    private transient SizeRequirements xTotal;
    private transient SizeRequirements yTotal;

    private transient PrintStream dbg;
}