1. Implement a Java application that has a border layout and labels for each reg

Question

1. Implement a Java application that has a border layout and labels for each region in the layout. Now defined mouse event to act as the following:

a. When mouse enters CENTER the program shows a dialog (Welcome to Riyadh)

b. When mouse enters WEST the program shows a dialog (Welcome to Jeddah)

c. When mouse enters SOUTH the program shows a dialog (Welcome to Abha)

d. When mouse enters NORTH the program shows a dialog (Welcome to Hail)

e. When mouse enters EAST the program shows a dialog (Welcome to Dhahran)

Explanation / Answer

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:

As a convenience, BorderLayout interprets the absence of a string specification the same as the constant 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 unpredicable 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:

Since:

JDK1.0

See Also:

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

oField Summary

Fields

Modifier and Type

Field and Description

static String

AFTER_LAST_LINE

Synonym for PAGE_END.

static String

AFTER_LINE_ENDS

Synonym for LINE_END.

static String

BEFORE_FIRST_LINE

Synonym for PAGE_START.

static String

BEFORE_LINE_BEGINS

Synonym for LINE_START.

static String

CENTER

The center layout constraint (middle of container).

static String

EAST

The east layout constraint (right side of container).

static String

LINE_END

The component goes at the end of the line direction for the layout.

static String

LINE_START

The component goes at the beginning of the line direction for the layout.

static String

NORTH

The north layout constraint (top of container).

static String

PAGE_END

The component comes after the last line of the layout's content.

static String

PAGE_START

The component comes before the first line of the layout's content.

static String

SOUTH

The south layout constraint (bottom of container).

static String

WEST

The west layout constraint (left side of container).

oConstructor Summary

Constructors

Constructor and 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.

oMethod Summary

Methods

Modifier and Type

Method and 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 inherited from class java.lang.Object

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

oField Detail

§NORTH

The north layout constraint (top of container).

See Also:

Constant Field Values

§SOUTH

The south layout constraint (bottom of container).

See Also:

Constant Field Values

§EAST

The east layout constraint (right side of container).

See Also:

Constant Field Values

§WEST

The west layout constraint (left side of container).

See Also:

Constant Field Values

§CENTER

The center layout constraint (middle of container).

See Also:

Constant Field Values

§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

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

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

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

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

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

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

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

oConstructor Detail

§BorderLayout

Constructs a new border layout with no gaps between components.

§BorderLayout

Parameters:

hgap - the horizontal gap.

vgap - the vertical gap.

oMethod Detail

§getHgap

Returns the horizontal gap between components.

Since:

JDK1.1

§setHgap

Sets the horizontal gap between components.

Parameters:

hgap - the horizontal gap between components

Since:

JDK1.1

§getVgap

Returns the vertical gap between components.

Since:

JDK1.1

§setVgap

Sets the vertical gap between components.

Parameters:

vgap - the vertical gap between components

Since:

JDK1.1

§addLayoutComponent

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)

§addLayoutComponent

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

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:

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

§getLayoutComponent

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:

addLayoutComponent(java.awt.Component, java.lang.Object)

§getLayoutComponent

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 of CENTER, NORTH, SOUTH, EAST, WEST

target - the Container used to obtain the constraint location based on the target Container'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

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

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:

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

§preferredLayoutSize

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:

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

§maximumLayoutSize

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)

§getLayoutAlignmentX

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

§getLayoutAlignmentY

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

§invalidateLayout

Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.

Specified by:

invalidateLayout in interface LayoutManager2

§layoutContainer

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:

Container, Container.doLayout()

§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.

Fields

Modifier and Type

Field and Description

static String

AFTER_LAST_LINE

Synonym for PAGE_END.

static String

AFTER_LINE_ENDS

Synonym for LINE_END.

static String

BEFORE_FIRST_LINE

Synonym for PAGE_START.

static String

BEFORE_LINE_BEGINS

Synonym for LINE_START.

static String

CENTER

The center layout constraint (middle of container).

static String

EAST

The east layout constraint (right side of container).

static String

LINE_END

The component goes at the end of the line direction for the layout.

static String

LINE_START

The component goes at the beginning of the line direction for the layout.

static String

NORTH

The north layout constraint (top of container).

static String

PAGE_END

The component comes after the last line of the layout's content.

static String

PAGE_START

The component comes before the first line of the layout's content.

static String

SOUTH

The south layout constraint (bottom of container).

static String

WEST

The west layout constraint (left side of container).

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