Class GridBagLayout

Class java.awt.GridBagLayout

Class Members | This Package | All Packages 
java.lang.Object
   |
   +----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:

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