Class GridBagLayout
Class java.awt.GridBagLayout
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java.lang.Object
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+----java.awt.GridBagLayout
public class GridBagLayout
extends Object
implements LayoutManager2, Serializable
The GridBagLayout class is a flexible layout
manager that aligns components 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 grid bag layout is associated
with an instance of
GridBagConstraints
that specifies how the component is laid out within its display area.
How a GridBagLayout object places a set of components
depends on the GridBagConstraints object associated
with each component, and on the minimum size
and the preferred size of the components' containers.
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:
- gridx,
gridy
- Specifies the cell at the upper left of the component's display area,
where the upper-left-most cell has address
gridx = 0,
gridy = 0.
Use GridBagConstraints.RELATIVE (the default value)
to specify that the component be just placed
just to the right of (for gridx)
or just below (for gridy)
the component that was added to the container
just before this component was added.
- gridwidth,
gridheight
- Specifies the number of cells in a row (for gridwidth)
or column (for gridheight)
in the component's display area.
The default value is 1.
Use GridBagConstraints.REMAINDER to specify
that the component be the last one in its row (for gridwidth)
or column (for gridheight).
Use GridBagConstraints.RELATIVE to specify
that the component be the next to last one
in its row (for gridwidth)
or column (for gridheight).
- fill
- Used when the component's display area
is larger than the component's requested size
to determine whether (and how) to resize the component.
Possible values are
GridBagConstraints.NONE (the default),
GridBagConstraints.HORIZONTAL
(make the component wide enough to fill its display area
horizontally, but don't change its height),
GridBagConstraints.VERTICAL
(make the component tall enough to fill its display area
vertically, but don't change its width), and
GridBagConstraints.BOTH
(make the component fill its display area entirely).
- ipadx,
ipady
- Specifies the component's internal padding within the layout,
how much to add to the minimum size of the component.
The width of the component will be at least its minimum width
plus (ipadx * 2) pixels (since the padding
applies to both sides of the component). Similarly, the height of
the component will be at least the minimum height plus
(ipady * 2) pixels.
- insets
- Specifies the component's external padding, the minimum
amount of space between the component and the edges of its display area.
- anchor
- Used when the component is smaller than its display area
to determine where (within the display area) to place the component.
Valid values are
GridBagConstraints.CENTER (the default),
GridBagConstraints.NORTH,
GridBagConstraints.NORTHEAST,
GridBagConstraints.EAST,
GridBagConstraints.SOUTHEAST,
GridBagConstraints.SOUTH,
GridBagConstraints.SOUTHWEST,
GridBagConstraints.WEST, and
GridBagConstraints.NORTHWEST.
- weightx,
weighty
- Used to determine how to distribute space, which is
important for specifying resizing behavior.
Unless you specify a weight for at least one component
in a row (weightx) and column (weighty),
all the components clump together in the center of their container.
This is because when the weight is zero (the default),
the GridBagLayout object puts any extra space
between its grid of cells and the edges of the container.
The following figure shows ten components (all buttons)
managed by a grid bag layout:
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:
- Button1, Button2, Button3: weightx = 1.0
- Button4: weightx = 1.0,
gridwidth = GridBagConstraints.REMAINDER
- Button5: gridwidth = GridBagConstraints.REMAINDER
- Button6: gridwidth = GridBagConstraints.RELATIVE
- Button7: gridwidth = GridBagConstraints.REMAINDER
- Button8: gridheight = 2,
weighty = 1.0
- Button9, Button 10:
gridwidth = GridBagConstraints.REMAINDER
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("Helvetica", 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();
}
}
- See Also:
- GridBagConstraints