java.awt
public class: BorderLayout [javadoc |
source]
java.lang.Object
java.awt.BorderLayout
All Implemented Interfaces:
LayoutManager2, java$io$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
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:
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);
}
}
| Field Summary |
|---|
| int | hgap | Constructs a border layout with the horizontal gaps
between components.
The horizontal gap is specified by hgap. |
| int | vgap | Constructs a border layout with the vertical gaps
between components.
The vertical gap is specified by vgap. |
| Component | north | Constant to specify components location to be the
north portion of the border layout. |
| Component | west | Constant to specify components location to be the
west portion of the border layout. |
| Component | east | Constant to specify components location to be the
east portion of the border layout. |
| Component | south | Constant to specify components location to be the
south portion of the border layout. |
| Component | center | Constant to specify components location to be the
center portion of the border layout. |
| Component | firstLine | A relative positioning constant, that can be used instead of
north, south, east, west or center.
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.
This will be the same for lastLine, firstItem, lastItem. |
| Component | lastLine | A relative positioning constant, that can be used instead of
north, south, east, west or center.
Please read Description for firstLine. |
| Component | firstItem | A relative positioning constant, that can be used instead of
north, south, east, west or center.
Please read Description for firstLine. |
| Component | lastItem | A relative positioning constant, that can be used instead of
north, south, east, west or center.
Please read Description for firstLine. |
| public static final String | NORTH | The north layout constraint (top of container). |
| public static final String | SOUTH | The south layout constraint (bottom of container). |
| public static final String | EAST | The east layout constraint (right side of container). |
| public static final String | WEST | The west layout constraint (left side of container). |
| public static final String | CENTER | The center layout constraint (middle of container). |
| public static final String | BEFORE_FIRST_LINE | Synonym for PAGE_START. Exists for compatibility with previous
versions. PAGE_START is preferred. |
| public static final String | AFTER_LAST_LINE | Synonym for PAGE_END. Exists for compatibility with previous
versions. PAGE_END is preferred. |
| public static final String | BEFORE_LINE_BEGINS | Synonym for LINE_START. Exists for compatibility with previous
versions. LINE_START is preferred. |
| public static final String | AFTER_LINE_ENDS | Synonym for LINE_END. Exists for compatibility with previous
versions. LINE_END is preferred. |
| 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.Also see:
- java.awt.Component#getComponentOrientation
- since:
1.4 -
|
| 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.Also see:
- java.awt.Component#getComponentOrientation
- since:
1.4 -
|
| 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.Also see:
- java.awt.Component#getComponentOrientation
- since:
1.4 -
|
| 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.Also see:
- java.awt.Component#getComponentOrientation
- since:
1.4 -
|
| Method from java.awt.BorderLayout Summary: |
|---|
|
addLayoutComponent, addLayoutComponent, getConstraints, getHgap, getLayoutAlignmentX, getLayoutAlignmentY, getLayoutComponent, getLayoutComponent, getVgap, invalidateLayout, layoutContainer, maximumLayoutSize, minimumLayoutSize, preferredLayoutSize, removeLayoutComponent, setHgap, setVgap, toString |
| Methods from java.lang.Object: |
|---|
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Method from java.awt.BorderLayout Detail: |
|---|
 public void addLayoutComponent(Component comp,
Object constraints) {
synchronized (comp.getTreeLock()) {
if ((constraints == null) || (constraints instanceof String)) {
addLayoutComponent((String)constraints, comp);
} else {
throw new IllegalArgumentException("cannot add to layout: constraint must be a string (or null)");
}
}
}
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. |
public void addLayoutComponent(String name,
Component comp) {
synchronized (comp.getTreeLock()) {
/* Special case: treat null the same as "Center". */
if (name == null) {
name = "Center";
}
/* Assign the component to one of the known regions of the layout.
*/
if ("Center".equals(name)) {
center = comp;
} else if ("North".equals(name)) {
north = comp;
} else if ("South".equals(name)) {
south = comp;
} else if ("East".equals(name)) {
east = comp;
} else if ("West".equals(name)) {
west = comp;
} else if (BEFORE_FIRST_LINE.equals(name)) {
firstLine = comp;
} else if (AFTER_LAST_LINE.equals(name)) {
lastLine = comp;
} else if (BEFORE_LINE_BEGINS.equals(name)) {
firstItem = comp;
} else if (AFTER_LINE_ENDS.equals(name)) {
lastItem = comp;
} else {
throw new IllegalArgumentException("cannot add to layout: unknown constraint: " + name);
}
}
} Deprecated! replaced - by addLayoutComponent(Component, Object).
|
public Object getConstraints(Component comp) {
//fix for 6242148 : API method java.awt.BorderLayout.getConstraints(null) should return null
if (comp == null){
return null;
}
if (comp == center) {
return CENTER;
} else if (comp == north) {
return NORTH;
} else if (comp == south) {
return SOUTH;
} else if (comp == west) {
return WEST;
} else if (comp == east) {
return EAST;
} else if (comp == firstLine) {
return PAGE_START;
} else if (comp == lastLine) {
return PAGE_END;
} else if (comp == firstItem) {
return LINE_START;
} else if (comp == lastItem) {
return LINE_END;
}
return null;
} Gets the constraints for the specified component |
public int getHgap() {
return hgap;
} Returns the horizontal gap between components. |
public float getLayoutAlignmentX(Container parent) {
return 0.5f;
} 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. |
public float getLayoutAlignmentY(Container parent) {
return 0.5f;
} 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. |
public Component getLayoutComponent(Object constraints) {
if (CENTER.equals(constraints)) {
return center;
} else if (NORTH.equals(constraints)) {
return north;
} else if (SOUTH.equals(constraints)) {
return south;
} else if (WEST.equals(constraints)) {
return west;
} else if (EAST.equals(constraints)) {
return east;
} else if (PAGE_START.equals(constraints)) {
return firstLine;
} else if (PAGE_END.equals(constraints)) {
return lastLine;
} else if (LINE_START.equals(constraints)) {
return firstItem;
} else if (LINE_END.equals(constraints)) {
return lastItem;
} else {
throw new IllegalArgumentException("cannot get component: unknown constraint: " + constraints);
}
} Gets the component that was added using the given constraint |
public Component getLayoutComponent(Container target,
Object constraints) {
boolean ltr = target.getComponentOrientation().isLeftToRight();
Component result = null;
if (NORTH.equals(constraints)) {
result = (firstLine != null) ? firstLine : north;
} else if (SOUTH.equals(constraints)) {
result = (lastLine != null) ? lastLine : south;
} else if (WEST.equals(constraints)) {
result = ltr ? firstItem : lastItem;
if (result == null) {
result = west;
}
} else if (EAST.equals(constraints)) {
result = ltr ? lastItem : firstItem;
if (result == null) {
result = east;
}
} else if (CENTER.equals(constraints)) {
result = center;
} else {
throw new IllegalArgumentException("cannot get component: invalid constraint: " + constraints);
}
return result;
} 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. |
public int getVgap() {
return vgap;
} Returns the vertical gap between components. |
public void invalidateLayout(Container target) {
} Invalidates the layout, indicating that if the layout manager
has cached information it should be discarded. |
public void layoutContainer(Container target) {
synchronized (target.getTreeLock()) {
Insets insets = target.getInsets();
int top = insets.top;
int bottom = target.height - insets.bottom;
int left = insets.left;
int right = target.width - insets.right;
boolean ltr = target.getComponentOrientation().isLeftToRight();
Component c = null;
if ((c=getChild(NORTH,ltr)) != null) {
c.setSize(right - left, c.height);
Dimension d = c.getPreferredSize();
c.setBounds(left, top, right - left, d.height);
top += d.height + vgap;
}
if ((c=getChild(SOUTH,ltr)) != null) {
c.setSize(right - left, c.height);
Dimension d = c.getPreferredSize();
c.setBounds(left, bottom - d.height, right - left, d.height);
bottom -= d.height + vgap;
}
if ((c=getChild(EAST,ltr)) != null) {
c.setSize(c.width, bottom - top);
Dimension d = c.getPreferredSize();
c.setBounds(right - d.width, top, d.width, bottom - top);
right -= d.width + hgap;
}
if ((c=getChild(WEST,ltr)) != null) {
c.setSize(c.width, bottom - top);
Dimension d = c.getPreferredSize();
c.setBounds(left, top, d.width, bottom - top);
left += d.width + hgap;
}
if ((c=getChild(CENTER,ltr)) != null) {
c.setBounds(left, top, right - left, bottom - top);
}
}
} 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. |
public Dimension maximumLayoutSize(Container target) {
return new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE);
} Returns the maximum dimensions for this layout given the components
in the specified target container. |
public Dimension minimumLayoutSize(Container target) {
synchronized (target.getTreeLock()) {
Dimension dim = new Dimension(0, 0);
boolean ltr = target.getComponentOrientation().isLeftToRight();
Component c = null;
if ((c=getChild(EAST,ltr)) != null) {
Dimension d = c.getMinimumSize();
dim.width += d.width + hgap;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(WEST,ltr)) != null) {
Dimension d = c.getMinimumSize();
dim.width += d.width + hgap;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(CENTER,ltr)) != null) {
Dimension d = c.getMinimumSize();
dim.width += d.width;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(NORTH,ltr)) != null) {
Dimension d = c.getMinimumSize();
dim.width = Math.max(d.width, dim.width);
dim.height += d.height + vgap;
}
if ((c=getChild(SOUTH,ltr)) != null) {
Dimension d = c.getMinimumSize();
dim.width = Math.max(d.width, dim.width);
dim.height += d.height + vgap;
}
Insets insets = target.getInsets();
dim.width += insets.left + insets.right;
dim.height += insets.top + insets.bottom;
return dim;
}
} 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. |
public Dimension preferredLayoutSize(Container target) {
synchronized (target.getTreeLock()) {
Dimension dim = new Dimension(0, 0);
boolean ltr = target.getComponentOrientation().isLeftToRight();
Component c = null;
if ((c=getChild(EAST,ltr)) != null) {
Dimension d = c.getPreferredSize();
dim.width += d.width + hgap;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(WEST,ltr)) != null) {
Dimension d = c.getPreferredSize();
dim.width += d.width + hgap;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(CENTER,ltr)) != null) {
Dimension d = c.getPreferredSize();
dim.width += d.width;
dim.height = Math.max(d.height, dim.height);
}
if ((c=getChild(NORTH,ltr)) != null) {
Dimension d = c.getPreferredSize();
dim.width = Math.max(d.width, dim.width);
dim.height += d.height + vgap;
}
if ((c=getChild(SOUTH,ltr)) != null) {
Dimension d = c.getPreferredSize();
dim.width = Math.max(d.width, dim.width);
dim.height += d.height + vgap;
}
Insets insets = target.getInsets();
dim.width += insets.left + insets.right;
dim.height += insets.top + insets.bottom;
return dim;
}
} 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. |
public void removeLayoutComponent(Component comp) {
synchronized (comp.getTreeLock()) {
if (comp == center) {
center = null;
} else if (comp == north) {
north = null;
} else if (comp == south) {
south = null;
} else if (comp == east) {
east = null;
} else if (comp == west) {
west = null;
}
if (comp == firstLine) {
firstLine = null;
} else if (comp == lastLine) {
lastLine = null;
} else if (comp == firstItem) {
firstItem = null;
} else if (comp == lastItem) {
lastItem = null;
}
}
} 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. |
public void setHgap(int hgap) {
this.hgap = hgap;
} Sets the horizontal gap between components. |
public void setVgap(int vgap) {
this.vgap = vgap;
} Sets the vertical gap between components. |
public String toString() {
return getClass().getName() + "[hgap=" + hgap + ",vgap=" + vgap + "]";
} Returns a string representation of the state of this border layout. |