javax.swing
Class BoxLayout

java.lang.Object
  javax.swing.BoxLayout

All Implemented Interfaces:

LayoutManager, LayoutManager2, Serializable

Direct Known Subclasses:

DefaultMenuLayout

public class BoxLayout

extends Object

implements LayoutManager2, Serializable

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.

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.

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^TM has been added to the java.beans package. Please see XMLEncoder.

Author:

Timothy Prinzing

See Also:

Box, ComponentOrientation, JComponent.getAlignmentX(), JComponent.getAlignmentY(), Serialized Form

Field Summary

private int	axis
private PrintStream	dbg
static int	LINE_AXIS Specifies that components should be laid out in the direction of a line of text as determined by the target container's ComponentOrientation property.
static int	PAGE_AXIS 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.
private Container	target
static int	X_AXIS Specifies that components should be laid out left to right.
private SizeRequirements[]	xChildren
private SizeRequirements	xTotal
static int	Y_AXIS Specifies that components should be laid out top to bottom.
private SizeRequirements[]	yChildren
private SizeRequirements	yTotal

Constructor Summary

	BoxLayout(Container target, int axis) Creates a layout manager that will lay out components along the given axis.
(package private)	BoxLayout(Container target, int axis, PrintStream dbg) Constructs a BoxLayout that produces debugging messages.

Method Summary

void	addLayoutComponent(Component comp, Object constraints) Not used by this class.
void	addLayoutComponent(String name, Component comp) Not used by this class.
(package private) void	checkContainer(Container target)
(package private) void	checkRequests()
float	getLayoutAlignmentX(Container target) Returns the alignment along the X axis for the container.
float	getLayoutAlignmentY(Container target) Returns the alignment along the Y axis for the container.
void	invalidateLayout(Container target) Indicates that a child has changed its layout related information, and thus any cached calculations should be flushed.
void	layoutContainer(Container target) Called by the AWT
Dimension	maximumLayoutSize(Container target) Returns the maximum dimensions the target container can use to lay out the components it contains.
Dimension	minimumLayoutSize(Container target) Returns the minimum dimensions needed to lay out the components contained in the specified target container.
Dimension	preferredLayoutSize(Container target) Returns the preferred dimensions for this layout, given the components in the specified target container.
void	removeLayoutComponent(Component comp) Not used by this class.
private int	resolveAxis(int axis, ComponentOrientation o) Given one of the 4 axis values, resolve it to an absolute axis.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

X_AXIS

public static final int X_AXIS

Specifies that components should be laid out left to right.

See Also:

Constant Field Values

Y_AXIS

public static final int Y_AXIS

Specifies that components should be laid out top to bottom.

See Also:

Constant Field Values

LINE_AXIS

public static final int LINE_AXIS

Specifies that components should be laid out in the direction of a line of text as determined by the target container's ComponentOrientation property.

See Also:

Constant Field Values

PAGE_AXIS

public static final int PAGE_AXIS

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.

See Also:

Constant Field Values

axis

private int axis

target

private Container target

xChildren

private transient SizeRequirements[] xChildren

yChildren

private transient SizeRequirements[] yChildren

xTotal

private transient SizeRequirements xTotal

yTotal

private transient SizeRequirements yTotal

dbg

private transient PrintStream dbg

Constructor Detail

BoxLayout

public BoxLayout(Container target,
                 int axis)

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

Parameters:

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

BoxLayout

BoxLayout(Container target,
          int axis,
          PrintStream dbg)

Constructs a BoxLayout that produces debugging messages.

Parameters:

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

Method Detail

invalidateLayout

public void invalidateLayout(Container target)

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.

Specified by:

invalidateLayout in interface LayoutManager2

Parameters:

target - the affected container

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

addLayoutComponent

public void addLayoutComponent(String name,
                               Component comp)

Not used by this class.

Specified by:

addLayoutComponent in interface LayoutManager

Parameters:

name - the name of the component

comp - the component

removeLayoutComponent

public void removeLayoutComponent(Component comp)

Not used by this class.

Specified by:

removeLayoutComponent in interface LayoutManager

Parameters:

comp - the component

addLayoutComponent

public void addLayoutComponent(Component comp,
                               Object constraints)

Not used by this class.

Specified by:

addLayoutComponent in interface LayoutManager2

Parameters:

comp - the component

constraints - constraints

preferredLayoutSize

public Dimension preferredLayoutSize(Container target)

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

Specified by:

preferredLayoutSize in interface LayoutManager

Parameters:

target - the container that needs to be laid out

Returns:

the dimensions >= 0 && <= Integer.MAX_VALUE

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

See Also:

Container, minimumLayoutSize(java.awt.Container), maximumLayoutSize(java.awt.Container)

minimumLayoutSize

public Dimension minimumLayoutSize(Container target)

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

Specified by:

minimumLayoutSize in interface LayoutManager

Parameters:

target - the container that needs to be laid out

Returns:

the dimensions >= 0 && <= Integer.MAX_VALUE

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

See Also:

preferredLayoutSize(java.awt.Container), maximumLayoutSize(java.awt.Container)

maximumLayoutSize

public Dimension maximumLayoutSize(Container target)

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

Specified by:

maximumLayoutSize in interface LayoutManager2

Parameters:

target - the container that needs to be laid out

Returns:

the dimenions >= 0 && <= Integer.MAX_VALUE

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

See Also:

preferredLayoutSize(java.awt.Container), minimumLayoutSize(java.awt.Container)

getLayoutAlignmentX

public float getLayoutAlignmentX(Container target)

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.

Specified by:

getLayoutAlignmentX in interface LayoutManager2

Parameters:

target - the container

Returns:

the alignment >= 0.0f && <= 1.0f

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

getLayoutAlignmentY

public float getLayoutAlignmentY(Container target)

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.

Specified by:

getLayoutAlignmentY in interface LayoutManager2

Parameters:

target - the container

Returns:

the alignment >= 0.0f && <= 1.0f

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

layoutContainer

public void layoutContainer(Container target)

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

Specified by:

layoutContainer in interface LayoutManager

Parameters:

target - the container to lay out

Throws:

AWTError - if the target isn't the container specified to the BoxLayout constructor

checkContainer

void checkContainer(Container target)

checkRequests

void checkRequests()

resolveAxis

private int resolveAxis(int axis,
                        ComponentOrientation o)

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.

Parameters:

axis - the axis to resolve

o - the ComponentOrientation to resolve against

Returns:

the resolved axis