JavaTM 2 Platform
Std. Ed. v1.3.1

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 layed 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 Box container uses BoxLayout (unlike JPanel, which defaults to flow layout). You can nest multiple boxes and add components to them to get the arrangement you want.

The BoxLayout manager that places each of its managed components from left to right or from top to bottom. When you create a BoxLayout, you specify whether its major axis is the X axis (which means left to right placement) or Y axis (top to bottom placement). Components are arranged from left to right (or top to bottom), in the same order as they were added to the container.

Instead of using BoxLayout directly, many programs use the Box class. The Box class provides a lightweight container that uses a BoxLayout. Box also provides handy methods to help you use BoxLayout well.

BoxLayout attempts to arrange components at their preferred widths (for left to right layout) or heights (for top to bottom layout). For a left to right 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 an 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.

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. A future release of Swing will provide support for long term persistence.

See Also:
Box, Component.getAlignmentX(), Component.getAlignmentY(), Serialized Form

Field Summary
static int X_AXIS
          Specifies that components should be laid out left to right.
static int Y_AXIS
          Specifies that components should be laid out top to bottom.
 
Constructor Summary
BoxLayout(Container target, int axis)
          Creates a layout manager that will lay out components either left to right or top to bottom, as specified in the axis parameter.
 
Method Summary
 void addLayoutComponent(Component comp, Object constraints)
          Not used by this class.
 void addLayoutComponent(String name, Component comp)
          Not used by this class.
 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 when the specified container needs to be laid out.
 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.
 
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.

Y_AXIS

public static final int Y_AXIS
Specifies that components should be laid out top to bottom.
Constructor Detail

BoxLayout

public BoxLayout(Container target,
                 int axis)
Creates a layout manager that will lay out components either left to right or top to bottom, as specified in the axis parameter.
Parameters:
target - the container that needs to be laid out
axis - the axis to lay out components along. For left-to-right layout, specify BoxLayout.X_AXIS; for top-to-bottom layout, specify BoxLayout.Y_AXIS
Throws:
AWTError - if the value of axis is invalid
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.
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

JavaTM 2 Platform
Std. Ed. v1.3.1

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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