BorderLayout
Class BorderLayout
- java.lang.Object
-
- java.awt.BorderLayout
- All Implemented Interfaces:
- LayoutManager, LayoutManager2, Serializable
public class BorderLayout extends Object implements 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 layed out.
NOTE: Currently (in the Java 2 platform v1.2), 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); } }
- Since:
- JDK1.0
- See Also:
-
Container.add(String, Component)
,ComponentOrientation
, Serialized Form
Fields
NORTH
public static final String NORTH
The north layout constraint (top of container).
SOUTH
public static final String SOUTH
The south layout constraint (bottom of container).
EAST
public static final String EAST
The east layout constraint (right side of container).
WEST
public static final String WEST
The west layout constraint (left side of container).
CENTER
public static final String CENTER
The center layout constraint (middle of container).
BEFORE_FIRST_LINE
public static final String BEFORE_FIRST_LINE
Synonym for PAGE_START. Exists for compatibility with previous versions. PAGE_START is preferred.
- Since:
- 1.2
- See Also:
-
PAGE_START
, Constant Field Values
AFTER_LAST_LINE
public static final String AFTER_LAST_LINE
Synonym for PAGE_END. Exists for compatibility with previous versions. PAGE_END is preferred.
- Since:
- 1.2
- See Also:
-
PAGE_END
, Constant Field Values
BEFORE_LINE_BEGINS
public static final String BEFORE_LINE_BEGINS
Synonym for LINE_START. Exists for compatibility with previous versions. LINE_START is preferred.
- Since:
- 1.2
- See Also:
-
LINE_START
, Constant Field Values
AFTER_LINE_ENDS
public static final String AFTER_LINE_ENDS
Synonym for LINE_END. Exists for compatibility with previous versions. LINE_END is preferred.
- Since:
- 1.2
- See Also:
-
LINE_END
, Constant Field Values
PAGE_START
public static final String PAGE_START
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.
- Since:
- 1.4
- See Also:
-
Component.getComponentOrientation()
, Constant Field Values
PAGE_END
public static final String PAGE_END
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.
- Since:
- 1.4
- See Also:
-
Component.getComponentOrientation()
, Constant Field Values
LINE_START
public static final String LINE_START
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.
- Since:
- 1.4
- See Also:
-
Component.getComponentOrientation()
, Constant Field Values
LINE_END
public static final String LINE_END
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.
- Since:
- 1.4
- See Also:
-
Component.getComponentOrientation()
, Constant Field Values
Constructors
BorderLayout
public BorderLayout()
Constructs a new border layout with no gaps between components.
BorderLayout
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
.
- Parameters:
-
hgap
- the horizontal gap. -
vgap
- the vertical gap.
Methods
getHgap
public int getHgap()
Returns the horizontal gap between components.
- Since:
- JDK1.1
setHgap
public void setHgap(int hgap)
Sets the horizontal gap between components.
- Parameters:
-
hgap
- the horizontal gap between components - Since:
- JDK1.1
getVgap
public int getVgap()
Returns the vertical gap between components.
- Since:
- JDK1.1
setVgap
public void setVgap(int vgap)
Sets the vertical gap between components.
- Parameters:
-
vgap
- the vertical gap between components - Since:
- JDK1.1
addLayoutComponent
public void addLayoutComponent(Component comp, Object constraints)
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.
- Specified by:
-
addLayoutComponent
in interfaceLayoutManager2
- Parameters:
-
comp
- the component to be added. -
constraints
- an object that specifies how and where the component is added to the layout. - Throws:
-
IllegalArgumentException
- if the constraint object is not a string, or if it not one of the five specified constants. - Since:
- JDK1.1
- See Also:
Container.add(java.awt.Component, java.lang.Object)
addLayoutComponent
@Deprecated public void addLayoutComponent(String name, Component comp)
Deprecated. replaced by addLayoutComponent(Component, Object)
.
Description copied from interface: LayoutManager
If the layout manager uses a per-component string, adds the component comp
to the layout, associating it with the string specified by name
.
- Specified by:
-
addLayoutComponent
in interfaceLayoutManager
- Parameters:
-
name
- the string to be associated with the component -
comp
- the component to be added
removeLayoutComponent
public void removeLayoutComponent(Component comp)
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.
- Specified by:
-
removeLayoutComponent
in interfaceLayoutManager
- Parameters:
-
comp
- the component to be removed. - See Also:
-
Container.remove(java.awt.Component)
,Container.removeAll()
getLayoutComponent
public Component getLayoutComponent(Object constraints)
Gets the component that was added using the given constraint
- Parameters:
-
constraints
- the desired constraint, one ofCENTER
,NORTH
,SOUTH
,WEST
,EAST
,PAGE_START
,PAGE_END
,LINE_START
,LINE_END
- Returns:
- the component at the given location, or
null
if the location is empty - Throws:
-
IllegalArgumentException
- if the constraint object is not one of the nine specified constants - Since:
- 1.5
- See Also:
addLayoutComponent(java.awt.Component, java.lang.Object)
getLayoutComponent
public Component getLayoutComponent(Container target, Object constraints)
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
.
- Parameters:
-
constraints
- the desired absolute position, one ofCENTER
,NORTH
,SOUTH
,EAST
,WEST
-
target
- theContainer
used to obtain the constraint location based on the targetContainer
's component orientation. - Returns:
- the component at the given location, or
null
if the location is empty - Throws:
-
IllegalArgumentException
- if the constraint object is not one of the five specified constants -
NullPointerException
- if the target parameter is null - Since:
- 1.5
- See Also:
addLayoutComponent(java.awt.Component, java.lang.Object)
getConstraints
public Object getConstraints(Component comp)
Gets the constraints for the specified component
- Parameters:
-
comp
- the component to be queried - Returns:
- the constraint for the specified component, or null if component is null or is not present in this layout
- Since:
- 1.5
- See Also:
addLayoutComponent(java.awt.Component, java.lang.Object)
minimumLayoutSize
public Dimension minimumLayoutSize(Container target)
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.
- Specified by:
-
minimumLayoutSize
in interfaceLayoutManager
- Parameters:
-
target
- the container in which to do the layout. - Returns:
- the minimum dimensions needed to lay out the subcomponents of the specified container.
- See Also:
-
Container
,preferredLayoutSize(java.awt.Container)
,Container.getMinimumSize()
preferredLayoutSize
public Dimension preferredLayoutSize(Container target)
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.
- Specified by:
-
preferredLayoutSize
in interfaceLayoutManager
- Parameters:
-
target
- the container in which to do the layout. - Returns:
- the preferred dimensions to lay out the subcomponents of the specified container.
- See Also:
-
Container
,minimumLayoutSize(java.awt.Container)
,Container.getPreferredSize()
maximumLayoutSize
public Dimension maximumLayoutSize(Container target)
Returns the maximum dimensions for this layout given the components in the specified target container.
- Specified by:
-
maximumLayoutSize
in interfaceLayoutManager2
- Parameters:
-
target
- the component which needs to be laid out - See Also:
-
Container
,minimumLayoutSize(java.awt.Container)
,preferredLayoutSize(java.awt.Container)
getLayoutAlignmentX
public float getLayoutAlignmentX(Container parent)
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.
- Specified by:
-
getLayoutAlignmentX
in interfaceLayoutManager2
getLayoutAlignmentY
public float getLayoutAlignmentY(Container parent)
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.
- Specified by:
-
getLayoutAlignmentY
in interfaceLayoutManager2
invalidateLayout
public void invalidateLayout(Container target)
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
- Specified by:
-
invalidateLayout
in interfaceLayoutManager2
layoutContainer
public void layoutContainer(Container target)
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.
- Specified by:
-
layoutContainer
in interfaceLayoutManager
- Parameters:
-
target
- the container in which to do the layout. - See Also:
-
Container
,Container.doLayout()
toString
public String toString()
Returns a string representation of the state of this border layout.
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