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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class BorderLayout - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.awt
Class BorderLayout

java.lang.Object
  |
  +--java.awt.BorderLayout

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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 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 four relative positioning constants, BEFORE_FIRST_LINE, AFTER_LAST_LINE, BEFORE_LINE_BEGINS, and AFTER_LINE_ENDS. In a container whose ComponentOrientation is set to ComponentOrientation.LEFT_TO_RIGHT, these constants map to NORTH, SOUTH, WEST, and EAST, respectively

Mixing the two types of constants can lead to unpredicable results. If you use both types, the relative constants will take precedence. For example, if you add components using both the NORTH and BEFORE_FIRST_LINE constants in a container whose orientation is LEFT_TO_RIGHT, only the BEFORE_FIRST_LINE will be layed out.

NOTE: Currently (in JDK 1.2), 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:

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 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);
   }
 }
 

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Since:

JDK1.0

See Also:

java.awt.Container.add(String, Component), ComponentOrientation, Serialized Form

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Field Summary
static String	AFTER_LAST_LINE           The component comes after the last line of the layout's content.
static String	AFTER_LINE_ENDS           The component goes at the end of the line direction for the layout.
static String	BEFORE_FIRST_LINE           The component comes before the first line of the layout's content.
static String	BEFORE_LINE_BEGINS           The component goes at the beginning of the line direction for the layout.
static String	CENTER           The center layout constraint (middle of container).
static String	EAST           The east layout constraint (right side of container).
static String	NORTH           The north layout constraint (top of container).
static String	SOUTH           The south layout constraint (bottom of container).
static String	WEST           The west layout constraint (left side of container).

 

Constructor Summary

BorderLayout()           Constructs a new border layout with no gaps between components.

BorderLayout(int hgap, int vgap)           Constructs a border layout with the specified gaps between components.

 

Method Summary
void	addLayoutComponent(Component comp, Object constraints)           Adds the specified component to the layout, using the specified constraint object.
void	addLayoutComponent(String name, Component comp)           Adds the specified component with the specified name to the layout.
int	getHgap()           Returns the horizontal gap between components.
float	getLayoutAlignmentX(Container parent)           Returns the alignment along the x axis.
float	getLayoutAlignmentY(Container parent)           Returns the alignment along the y axis.
int	getVgap()           Returns the vertical gap between components.
void	invalidateLayout(Container target)           Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
void	layoutContainer(Container target)           Lays out the container argument using this border layout.
Dimension	maximumLayoutSize(Container target)           Returns the maximum dimensions for this layout given the components in the specified target container.
Dimension	minimumLayoutSize(Container target)           Determines the minimum size of the target container using this layout manager.
Dimension	preferredLayoutSize(Container target)           Determines the preferred size of the target container using this layout manager, based on the components in the container.
void	removeLayoutComponent(Component comp)           Removes the specified component from this border layout.
void	setHgap(int hgap)           Sets the horizontal gap between components.
void	setVgap(int vgap)           Sets the vertical gap between components.
String	toString()           Returns a string representation of the state of this border layout.

 

Methods inherited from class java.lang.Object

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

 

Field Detail

NORTH

public static final String NORTH

The north layout constraint (top of container).

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SOUTH

public static final String SOUTH

The south layout constraint (bottom of container).

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EAST

public static final String EAST

The east layout constraint (right side of container).

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WEST

public static final String WEST

The west layout constraint (left side of container).

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CENTER

public static final String CENTER

The center layout constraint (middle of container).

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BEFORE_FIRST_LINE

public static final String BEFORE_FIRST_LINE

The component comes before the first line of the layout's content. For Western, top-to-bottom, left-to-right orientations, this is equivalent to NORTH.

See Also:

Component.getComponentOrientation()

Since:

JDK1.2

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AFTER_LAST_LINE

public static final String AFTER_LAST_LINE

The component comes after the last line of the layout's content. For Western, top-to-bottom, left-to-right orientations, this is equivalent to SOUTH.

See Also:

Component.getComponentOrientation()

Since:

JDK1.2

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BEFORE_LINE_BEGINS

public static final String BEFORE_LINE_BEGINS

The component goes at the beginning of the line direction for the layout. For Western, top-to-bottom, left-to-right orientations, this is equivalent to WEST.

See Also:

Component.getComponentOrientation()

Since:

JDK1.2

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AFTER_LINE_ENDS

public static final String AFTER_LINE_ENDS

The component goes at the end of the line direction for the layout. For Western, top-to-bottom, left-to-right orientations, this is equivalent to EAST.

See Also:

Component.getComponentOrientation()

Since:

JDK1.2

Constructor Detail

BorderLayout

public BorderLayout()

Constructs a new border layout with no gaps between components.

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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.

Method Detail

getHgap

public int getHgap()

Returns the horizontal gap between components.

Since:

JDK1.1

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setHgap

public void setHgap(int hgap)

Sets the horizontal gap between components.

Parameters:

hgap - the horizontal gap between components

Since:

JDK1.1

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getVgap

public int getVgap()

Returns the vertical gap between components.

Since:

JDK1.1

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setVgap

public void setVgap(int vgap)

Sets the vertical gap between components.

Parameters:

vgap - the vertical gap between components

Since:

JDK1.1

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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 interface LayoutManager2

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)

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addLayoutComponent

public void addLayoutComponent(String name,
                               Component comp)

Deprecated. replaced by addLayoutComponent(Component, Object).

Description copied from interface: LayoutManager

Adds the specified component with the specified name to the layout.

Tags copied from interface: LayoutManager

Parameters:

name - the component name

comp - the component to be added

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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.

Parameters:

comp - the component to be removed.

See Also:

Container.remove(java.awt.Component), Container.removeAll()

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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.

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()

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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.

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()

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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 interface LayoutManager2

Parameters:

target - the component which needs to be laid out

See Also:

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

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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 interface LayoutManager2

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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 interface LayoutManager2

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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 interface LayoutManager2

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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.

Parameters:

target - the container in which to do the layout.

See Also:

Container, Container.doLayout()

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toString

public String toString()

Returns a string representation of the state of this border layout.

Overrides:

toString in class Object

Returns:

a string representation of this border layout.

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