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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 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:

Diagram of an applet
demonstrating BorderLayout. Each section of the BorderLayout contains a
Button corresponding to its position in the layout, one of: North, West,
Center, East, or South.

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:

1.0

See Also:

Field Summary

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

Constructor Summary

Constructor	Description
`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

Modifier and Type	Method	Description
`void`	`addLayoutComponent(Component comp, Object constraints)`	Adds the specified component to the layout, using the specified constraint object.
`void`	`addLayoutComponent(String name, Component comp)`	Deprecated. replaced by `addLayoutComponent(Component, Object)`.
`Object`	`getConstraints(Component comp)`	Gets the constraints for the specified component
`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.
`Component`	`getLayoutComponent(Container target, Object constraints)`	Returns the component that corresponds to the given constraint location based on the target `Container`'s component orientation.
`Component`	`getLayoutComponent(Object constraints)`	Gets the component that was added using the given constraint
`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 declared in class java.lang.Object

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

Field Details

NORTH

public static final String NORTH

The north layout constraint (top of container).

See Also:

SOUTH

public static final String SOUTH

The south layout constraint (bottom of container).

See Also:

EAST

public static final String EAST

The east layout constraint (right side of container).

See Also:

WEST

public static final String WEST

The west layout constraint (left side of container).

See Also:

CENTER

public static final String CENTER

The center layout constraint (middle of container).

See Also:

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:

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:

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:

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:

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:

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:

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:

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:

Constructor Details

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.

Method Details

getHgap

public int getHgap()

Returns the horizontal gap between components.

Returns:: the horizontal gap between components
Since:: 1.1

setHgap

public void setHgap(int hgap)

Sets the horizontal gap between components.

Parameters:: hgap - the horizontal gap between components
Since:: 1.1

getVgap

public int getVgap()

Returns the vertical gap between components.

Returns:: the vertical gap between components
Since:: 1.1

setVgap

public void setVgap(int vgap)

Sets the vertical gap between components.

Parameters:: vgap - the vertical gap between components
Since:: 1.1

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 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:

1.1

See Also:

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 interface LayoutManager
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 interface LayoutManager

Parameters:

comp - the component to be removed.

See Also:

getLayoutComponent

public Component getLayoutComponent(Object constraints)

Gets the component that was added using the given constraint

Parameters:

constraints - the desired constraint, one of CENTER, 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:

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:

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

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:

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:

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 interface LayoutManager

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:

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 interface LayoutManager

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:

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

Returns:

the maximum size of the container

See Also:

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
Parameters:: parent - the target container
Returns:: the x-axis alignment preference

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
Parameters:: parent - the target container
Returns:: the y-axis alignment preference

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
Parameters:: target - the target container

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 interface LayoutManager

Parameters:

target - the container in which to do the layout.

See Also:

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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