is new.
java.lang.Objectjava.awt.GridBagLayout
public class GridBagLayout
The GridBagLayout class is a flexible layout manager that aligns components
vertically, horizontally or along their baseline
vertically and horizontally,
without requiring that the components be of the same size. Each GridBagLayout object maintains a dynamic, rectangular grid of cells, with each component occupying one or more cells, called its display area.
Each component managed by a GridBagLayout is associated with an instance of GridBagConstraints . The constraints object specifies where a component's display area should be located on the grid and how the component should be positioned within its display area. In addition to its constraints object, the GridBagLayout also considers each component's minimum and preferred sizes in order to determine a component's size.
The overall orientation of the grid depends on the container's ComponentOrientation property. For horizontal left-to-right orientations, grid coordinate (0,0) is in the upper left corner of the container with x increasing to the right and y increasing downward. For horizontal right-to-left orientations, grid coordinate (0,0) is in the upper right corner of the container with x increasing to the left and y increasing downward.
To use a grid bag layout effectively, you must customize one or more of the GridBagConstraints objects that are associated with its components. You customize a GridBagConstraints object by setting one or more of its instance variables:
Specifies where
should be positioned in
area.
three
absolute, orientation-relative,
baseline-relative Orientation relative
Baseline relative values are calculated relative to the baseline.
Valid values are:
Each row may have a baseline; the baseline is determined by the components in that row that have a valid baseline and are aligned along the baseline (the component's anchor value is one of BASELINE, BASELINE_LEADING or BASELINE_TRAILING). If none of the components in the row has a valid baseline, the row does not have a baseline.
The following figures show ten components (all buttons) managed by a grid bag layout. Figure 1 shows the layout for a horizontal, left-to-right container and Figure 2 shows the layout for a horizontal, right-to-left container.
If a component spans rows it is aligned either to the baseline of the start row (if the baseline-resize behavior is CONSTANT_ASCENT) or the end row (if the baseline-resize behavior is CONSTANT_DESCENT). The row that the component is aligned to is called the prevailing row.
The following figure shows a baseline layout and includes a component that spans rows:
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This layout consists of three components:
A panel that starts in row 0 and ends in row 1. The panel has a baseline-resize behavior of CONSTANT_DESCENT and has an anchor of BASELINE. As the baseline-resize behavior is CONSTANT_DESCENT the prevailing row for the panel is row 1.
Two buttons, each with a baseline-resize behavior of CENTER_OFFSET and an anchor of BASELINE.
Because the second button and the panel share the same prevailing row, they are both aligned along their baseline.
Components positioned using one of the baseline-relative values resize differently than when positioned using an absolute or orientation-relative value. How components change is dictated by how the baseline of the prevailing row changes. The baseline is anchored to the bottom of the display area if any components with the same prevailing row have a baseline-resize behavior of CONSTANT_DESCENT, otherwise the baseline is anchored to the top of the display area. The following rules dictate the resize behavior:
Resizable components positioned above the baseline can only grow as tall as the baseline. For example, if the baseline is at 100 and anchored at the top, a resizable component positioned above the baseline can never grow more than 100 units.
Similarly, resizable components positioned below the baseline can only grow as high as the difference between the display height and the baseline.
Resizable components positioned on the baseline with a baseline-resize behavior of OTHER are only resized if the baseline at the resized size fits within the display area. If the baseline is such that it does not fit within the display area the component is not resized.
Components positioned on the baseline that do not have a baseline-resize behavior of OTHER can only grow as tall as display height - baseline + baseline of component.
If you position a component along the baseline, but the component does not have a valid baseline, it will be vertically centered in its space. Similarly if you have positioned a component relative to the baseline and none of the components in the row have a valid baseline the component is vertically centered.
The following figures show ten components (all buttons) managed by a grid bag layout. Figure 2 shows the layout for a horizontal, left-to-right container and Figure 3 shows the layout for a horizontal, right-to-left container.
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Figure 2: Horizontal, Left-to-Right
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Figure 3: Horizontal, Right-to-Left
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Each of the ten components has the fill field of its associated GridBagConstraints object set to GridBagConstraints.BOTH. In addition, the components have the following non-default constraints:
Here is the code that implements the example shown above:
import java.awt.*;
import java.util.*;
import java.applet.Applet;
public class GridBagEx1 extends Applet {
protected void makebutton(String name,
GridBagLayout gridbag,
GridBagConstraints c) {
Button button = new Button(name);
gridbag.setConstraints(button, c);
add(button);
}
public void init() {
GridBagLayout gridbag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
setFont(new Font("SansSerif", Font.PLAIN, 14));
setLayout(gridbag);
c.fill = GridBagConstraints.BOTH;
c.weightx = 1.0;
makebutton("Button1", gridbag, c);
makebutton("Button2", gridbag, c);
makebutton("Button3", gridbag, c);
c.gridwidth = GridBagConstraints.REMAINDER; //end row
makebutton("Button4", gridbag, c);
c.weightx = 0.0; //reset to the default
makebutton("Button5", gridbag, c); //another row
c.gridwidth = GridBagConstraints.RELATIVE; //next-to-last in row
makebutton("Button6", gridbag, c);
c.gridwidth = GridBagConstraints.REMAINDER; //end row
makebutton("Button7", gridbag, c);
c.gridwidth = 1; //reset to the default
c.gridheight = 2;
c.weighty = 1.0;
makebutton("Button8", gridbag, c);
c.weighty = 0.0; //reset to the default
c.gridwidth = GridBagConstraints.REMAINDER; //end row
c.gridheight = 1; //reset to the default
makebutton("Button9", gridbag, c);
makebutton("Button10", gridbag, c);
setSize(300, 100);
}
public static void main(String args[]) {
Frame f = new Frame("GridBag Layout Example");
GridBagEx1 ex1 = new GridBagEx1();
ex1.init();
f.add("Center", ex1);
f.pack();
f.setSize(f.getPreferredSize());
f.show();
}
}
| Field Summary | |
|---|---|
| double[] |
columnWeights
This field holds the overrides to the column weights. |
| int[] |
columnWidths
This field holds the overrides to the column minimum width. |
| protected Hashtable < Component , GridBagConstraints > |
comptable
This hashtable maintains the association between a component and its gridbag constraints. |
| protected GridBagConstraints |
defaultConstraints
This field holds a gridbag constraints instance containing the default values, so if a component does not have gridbag constraints associated with it, then the component will be assigned a copy of the defaultConstraints. |
| protected java.awt.GridBagLayoutInfo |
layoutInfo
This field holds the layout information for the gridbag. |
| protected static int |
MAXGRIDSIZE
This field is no longer used to reserve arrays and keeped for backward compatibility.
|
| protected static int |
MINSIZE
The smallest grid that can be laid out by the grid bag layout. |
| protected static int |
PREFERREDSIZE
The preferred grid size that can be laid out by the grid bag layout. |
| int[] |
rowHeights
This field holds the overrides to the row minimum heights. |
| double[] |
rowWeights
This field holds the overrides to the row weights. |
| Constructor Summary | |
|---|---|
|
GridBagLayout
() Creates a grid bag layout manager. |
|
| Method Summary | |
|---|---|
| void |
addLayoutComponent
(
Component
comp,
Object
constraints) Adds the specified component to the layout, using the specified constraints object. |
| void |
addLayoutComponent
(
String
name,
Component
comp) Has no effect, since this layout manager does not use a per-component string. |
| protected void |
adjustForGravity
(
GridBagConstraints
constraints,
Rectangle
r) Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads. |
| protected void |
AdjustForGravity
(
GridBagConstraints
constraints,
Rectangle
r) This method is obsolete and supplied for backwards compatability only; new code should call adjustForGravity instead. |
| protected void |
arrangeGrid
(
Container
parent) Lays out the grid. |
| protected void |
ArrangeGrid
(
Container
parent) This method is obsolete and supplied for backwards compatability only; new code should call arrangeGrid instead. |
| GridBagConstraints |
getConstraints
(
Component
comp) Gets the constraints for the specified component. |
| float |
getLayoutAlignmentX
(
Container
parent) Returns the alignment along the x axis. |
| float |
getLayoutAlignmentY
(
Container
parent) Returns the alignment along the y axis. |
| int[][] |
getLayoutDimensions
() Determines column widths and row heights for the layout grid. |
| protected java.awt.GridBagLayoutInfo |
getLayoutInfo
(
Container
parent, int sizeflag) Fills in an instance of GridBagLayoutInfo for the current set of managed children. |
| protected java.awt.GridBagLayoutInfo |
GetLayoutInfo
(
Container
parent, int sizeflag) This method is obsolete and supplied for backwards compatability only; new code should call getLayoutInfo instead. |
| Point |
getLayoutOrigin
() Determines the origin of the layout area, in the graphics coordinate space of the target container. |
| double[][] |
getLayoutWeights
() Determines the weights of the layout grid's columns and rows. |
| protected Dimension |
getMinSize
(
Container
parent, java.awt.GridBagLayoutInfo info) Figures out the minimum size of the master based on the information from getLayoutInfo. |
| protected Dimension |
GetMinSize
(
Container
parent, java.awt.GridBagLayoutInfo info) This method is obsolete and supplied for backwards compatability only; new code should call getMinSize instead. |
| void |
invalidateLayout
(
Container
target) Invalidates the layout, indicating that if the layout manager has cached information it should be discarded. |
| void |
layoutContainer
(
Container
parent) Lays out the specified container using this grid bag layout. |
| Point |
location
(int x, int y) Determines which cell in the layout grid contains the point specified by (x, y). |
| protected GridBagConstraints |
lookupConstraints
(
Component
comp) Retrieves the constraints for the specified component. |
| Dimension |
maximumLayoutSize
(
Container
target) Returns the maximum dimensions for this layout given the components in the specified target container. |
| Dimension |
minimumLayoutSize
(
Container
parent) Determines the minimum size of the parent container using this grid bag layout. |
| Dimension |
preferredLayoutSize
(
Container
parent) Determines the preferred size of the parent container using this grid bag layout. |
| void |
removeLayoutComponent
(
Component
comp) Removes the specified component from this layout. |
| void |
setConstraints
(
Component
comp,
GridBagConstraints
constraints) Sets the constraints for the specified component in this layout. |
| String |
toString
() Returns a string representation of this grid bag layout's values. |
| Methods inherited from class java.lang. Object |
|---|
| clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
| Field Detail |
|---|
protected static final int MAXGRIDSIZE
This field is no longer used to reserve arrays and keeped for backward compatibility. Previously, this was the maximum number of grid positions (both horizontal and vertical) that could be laid out by the grid bag layout. Current implementation doesn't impose any limits on the size of a grid.
protected static final int MINSIZE
protected static final int PREFERREDSIZE
protected Hashtable<Component,GridBagConstraints> comptable
protected GridBagConstraints defaultConstraints
protected java.awt.GridBagLayoutInfo layoutInfo
public int[] columnWidths
public int[] rowHeights
public double[] columnWeights
public double[] rowWeights
| Constructor Detail |
|---|
public GridBagLayout()
| Method Detail |
|---|
public void setConstraints(Component comp,
GridBagConstraints constraints)
public GridBagConstraints getConstraints(Component comp)
protected GridBagConstraints lookupConstraints(Component comp)
If comp is not in the GridBagLayout, a set of default GridBagConstraints are returned. A comp value of null is invalid and returns null.
public Point getLayoutOrigin()
public int[][] getLayoutDimensions()
Most applications do not call this method directly.
public double[][] getLayoutWeights()
Most applications do not call this method directly.
public Point location(int x,
int y)
If the (x, y) point lies outside the grid, the following rules are used. The column index is returned as zero if x lies to the left of the layout for a left-to-right container or to the right of the layout for a right-to-left container. The column index is returned as the number of columns if x lies to the right of the layout in a left-to-right container or to the left in a right-to-left container. The row index is returned as zero if y lies above the layout, and as the number of rows if y lies below the layout. The orientation of a container is determined by its ComponentOrientation property.
public void addLayoutComponent(String name,
Component comp)
public void addLayoutComponent(Component comp,
Object constraints)
public void removeLayoutComponent(Component comp)
Most applications do not call this method directly.
public Dimension preferredLayoutSize(Container parent)
Most applications do not call this method directly.
public Dimension minimumLayoutSize(Container parent)
Most applications do not call this method directly.
public Dimension maximumLayoutSize(Container target)
public float getLayoutAlignmentX(Container parent)
public float getLayoutAlignmentY(Container parent)
public void invalidateLayout(Container target)
public void layoutContainer(Container parent)
Most applications do not call this method directly.
public String toString()
protected java.awt.GridBagLayoutInfo getLayoutInfo(Container parent,
int sizeflag)
This method should only be used internally by GridBagLayout.
protected java.awt.GridBagLayoutInfo GetLayoutInfo(Container parent,
int sizeflag)
protected void adjustForGravity(GridBagConstraints constraints,
Rectangle r)
protected void AdjustForGravity(GridBagConstraints constraints,
Rectangle r)
protected Dimension getMinSize(Container parent,
java.awt.GridBagLayoutInfo info)
protected Dimension GetMinSize(Container parent,
java.awt.GridBagLayoutInfo info)
protected void arrangeGrid(Container parent)
protected void ArrangeGrid(Container parent)