LayoutManager
, LayoutManager2
, Serializable
A border layout lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center. Each region may contain no more than one component, and is identified by a corresponding constant:
NORTH
,
SOUTH
,
EAST
,
WEST
, and
CENTER
. When adding a component to a container with a border layout, use one of these five constants, for example:
Panel p = new Panel(); p.setLayout(new BorderLayout()); p.add(new Button("Okay"), BorderLayout.SOUTH);
As a convenience,
BorderLayout
interprets the absence of a string specification the same as the constant
CENTER
:
Panel p2 = new Panel(); p2.setLayout(new BorderLayout()); p2.add(new TextArea()); // Same as p.add(new TextArea(), BorderLayout.CENTER);
In addition, BorderLayout
supports the relative positioning constants, PAGE_START
, PAGE_END
, LINE_START
, and LINE_END
. In a container whose ComponentOrientation
is set to ComponentOrientation.LEFT_TO_RIGHT
, these constants map to NORTH
, SOUTH
, WEST
, and EAST
, respectively.
For compatibility with previous releases, BorderLayout
also includes the relative positioning constants BEFORE_FIRST_LINE
, AFTER_LAST_LINE
, BEFORE_LINE_BEGINS
and AFTER_LINE_ENDS
. These are equivalent to PAGE_START
, PAGE_END
, LINE_START
and LINE_END
respectively. For consistency with the relative positioning constants used by other components, the latter constants are preferred.
Mixing both absolute and relative positioning constants can lead to unpredictable results. If you use both types, the relative constants will take precedence. For example, if you add components using both the NORTH
and PAGE_START
constants in a container whose orientation is LEFT_TO_RIGHT
, only the PAGE_START
will be laid out.
NOTE: Currently, BorderLayout
does not support vertical orientations. The isVertical
setting on the container's ComponentOrientation
is not respected.
The components are laid out according to their preferred sizes and the constraints of the container's size. The NORTH
and SOUTH
components may be stretched horizontally; the EAST
and WEST
components may be stretched vertically; the CENTER
component may stretch both horizontally and vertically to fill any space left over.
Here is an example of five buttons in an applet laid out using the BorderLayout
layout manager:
The code for this applet is as follows:
import java.awt.*; import java.applet.Applet; public class buttonDir extends Applet { public void init() { setLayout(new BorderLayout()); add(new Button("North"), BorderLayout.NORTH); add(new Button("South"), BorderLayout.SOUTH); add(new Button("East"), BorderLayout.EAST); add(new Button("West"), BorderLayout.WEST); add(new Button("Center"), BorderLayout.CENTER); } }
Fields
The center layout constraint (middle of container).
The east layout constraint (right side of container).
The component goes at the end of the line direction for the layout.
The component goes at the beginning of the line direction for the layout.
The north layout constraint (top of container).
The component comes after the last line of the layout's content.
The component comes before the first line of the layout's content.
The south layout constraint (bottom of container).
The west layout constraint (left side of container).
Constructors
Constructs a new border layout with no gaps between components.
Constructs a border layout with the specified gaps between components.
void
Adds the specified component to the layout, using the specified constraint object.
void
Gets the constraints for the specified component
int
Returns the horizontal gap between components.
float
Returns the alignment along the x axis.
float
Returns the alignment along the y axis.
Returns the component that corresponds to the given constraint location based on the target Container
's component orientation.
Gets the component that was added using the given constraint
int
Returns the vertical gap between components.
void
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
void
Lays out the container argument using this border layout.
Returns the maximum dimensions for this layout given the components in the specified target container.
Determines the minimum size of the target
container using this layout manager.
Determines the preferred size of the target
container using this layout manager, based on the components in the container.
void
Removes the specified component from this border layout.
void
Sets the horizontal gap between components.
void
Sets the vertical gap between components.
Returns a string representation of the state of this border layout.
The north layout constraint (top of container).
The south layout constraint (bottom of container).
The east layout constraint (right side of container).
The west layout constraint (left side of container).
The center layout constraint (middle of container).
Synonym for PAGE_START. Exists for compatibility with previous versions. PAGE_START is preferred.
Synonym for PAGE_END. Exists for compatibility with previous versions. PAGE_END is preferred.
Synonym for LINE_START. Exists for compatibility with previous versions. LINE_START is preferred.
Synonym for LINE_END. Exists for compatibility with previous versions. LINE_END is preferred.
The component comes before the first line of the layout's content. For Western, left-to-right and top-to-bottom orientations, this is equivalent to NORTH.
The component comes after the last line of the layout's content. For Western, left-to-right and top-to-bottom orientations, this is equivalent to SOUTH.
The component goes at the beginning of the line direction for the layout. For Western, left-to-right and top-to-bottom orientations, this is equivalent to WEST.
The component goes at the end of the line direction for the layout. For Western, left-to-right and top-to-bottom orientations, this is equivalent to EAST.
public BorderLayout()
Constructs a new border layout with no gaps between components.
public BorderLayout(int hgap, int vgap)
Constructs a border layout with the specified gaps between components. The horizontal gap is specified by hgap
and the vertical gap is specified by vgap
.
hgap
- the horizontal gap.
vgap
- the vertical gap.
public int getHgap()
Returns the horizontal gap between components.
public void setHgap(int hgap)
Sets the horizontal gap between components.
hgap
- the horizontal gap between components
public int getVgap()
Returns the vertical gap between components.
public void setVgap(int vgap)
Sets the vertical gap between components.
vgap
- the vertical gap between components
Adds the specified component to the layout, using the specified constraint object. For border layouts, the constraint must be one of the following constants:
NORTH
,
SOUTH
,
EAST
,
WEST
, or
CENTER
.
Most applications do not call this method directly. This method is called when a component is added to a container using the Container.add
method with the same argument types.
addLayoutComponent
in interface LayoutManager2
comp
- the component to be added.
constraints
- an object that specifies how and where the component is added to the layout.
IllegalArgumentException
- if the constraint object is not a string, or if it not one of the five specified constants.
If the layout manager uses a per-component string, adds the component comp
to the layout, associating it with the string specified by name
.
addLayoutComponent
in interface LayoutManager
name
- the string to be associated with the component
comp
- the component to be added
Removes the specified component from this border layout. This method is called when a container calls its remove
or removeAll
methods. Most applications do not call this method directly.
removeLayoutComponent
in interface LayoutManager
comp
- the component to be removed.
Gets the component that was added using the given constraint
constraints
- the desired constraint, one of CENTER
, NORTH
, SOUTH
, WEST
, EAST
, PAGE_START
, PAGE_END
, LINE_START
, LINE_END
null
if the location is empty
IllegalArgumentException
- if the constraint object is not one of the nine specified constants
Returns the component that corresponds to the given constraint location based on the target Container
's component orientation. Components added with the relative constraints PAGE_START
, PAGE_END
, LINE_START
, and LINE_END
take precedence over components added with the explicit constraints NORTH
, SOUTH
, WEST
, and EAST
. The Container
's component orientation is used to determine the location of components added with LINE_START
and LINE_END
.
target
- the Container
used to obtain the constraint location based on the target Container
's component orientation.
constraints
- the desired absolute position, one of CENTER
, NORTH
, SOUTH
, EAST
, WEST
null
if the location is empty
IllegalArgumentException
- if the constraint object is not one of the five specified constants
NullPointerException
- if the target parameter is null
Gets the constraints for the specified component
comp
- the component to be queried
Determines the minimum size of the
target
container using this layout manager.
This method is called when a container calls its getMinimumSize
method. Most applications do not call this method directly.
minimumLayoutSize
in interface LayoutManager
target
- the container in which to do the layout.
Determines the preferred size of the
target
container using this layout manager, based on the components in the container.
Most applications do not call this method directly. This method is called when a container calls its getPreferredSize
method.
preferredLayoutSize
in interface LayoutManager
target
- the container in which to do the layout.
Returns the maximum dimensions for this layout given the components in the specified target container.
maximumLayoutSize
in interface LayoutManager2
target
- the component which needs to be laid out
Returns the alignment along the x axis. This specifies how the component would like to be aligned relative to other components. The value should be a number between 0 and 1 where 0 represents alignment along the origin, 1 is aligned the furthest away from the origin, 0.5 is centered, etc.
getLayoutAlignmentX
in interface LayoutManager2
parent
- the target container
Returns the alignment along the y axis. This specifies how the component would like to be aligned relative to other components. The value should be a number between 0 and 1 where 0 represents alignment along the origin, 1 is aligned the furthest away from the origin, 0.5 is centered, etc.
getLayoutAlignmentY
in interface LayoutManager2
parent
- the target container
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
invalidateLayout
in interface LayoutManager2
target
- the target container
Lays out the container argument using this border layout.
This method actually reshapes the components in the specified container in order to satisfy the constraints of this BorderLayout
object. The NORTH
and SOUTH
components, if any, are placed at the top and bottom of the container, respectively. The WEST
and EAST
components are then placed on the left and right, respectively. Finally, the CENTER
object is placed in any remaining space in the middle.
Most applications do not call this method directly. This method is called when a container calls its doLayout
method.
layoutContainer
in interface LayoutManager
target
- the container in which to do the layout.
Returns a string representation of the state of this border layout.
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