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Class java.awt.GridBagLayout

java.lang.Object
|
   +----java.awt.GridBagLayout

public class GridBagLayout

extends Object

implements LayoutManager2, Serializable

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

columnWeights

columnWidths

comptable

defaultConstraints

layoutInfo

MAXGRIDSIZE

The maximum number of grid positions (both horizontally and vertically) that can be laid out by the grid bag layout.

MINSIZE

The smallest grid that can be laid out by the grid bag layout.

PREFERREDSIZE

rowHeights

rowWeights

GridBagLayout()

Creates a grid bag layout manager.

addLayoutComponent(Component, Object)

Adds the specified component to the layout, using the specified constraint object.

addLayoutComponent(String, Component)

Adds the specified component with the specified name to the layout.

AdjustForGravity(GridBagConstraints, Rectangle)

ArrangeGrid(Container)

getConstraints(Component)

Gets the constraints for the specified component.

getLayoutAlignmentX(Container)

Returns the alignment along the x axis.

getLayoutAlignmentY(Container)

Returns the alignment along the y axis.

getLayoutDimensions()

Determines column widths and row heights for the layout grid.

GetLayoutInfo(Container, int)

Print the layout constraints.

getLayoutOrigin()

Determines the origin of the layout grid.

getLayoutWeights()

Determines the weights of the layout grid's columns and rows.

GetMinSize(Container, GridBagLayoutInfo)

invalidateLayout(Container)

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

layoutContainer(Container)

Lays out the specified container using this grid bag layout.

location(int, int)

Determines which cell in the layout grid contains the point specified by (x, y).

lookupConstraints(Component)

Retrieves the constraints for the specified component.

maximumLayoutSize(Container)

Returns the maximum dimensions for this layout given the components in the specified target container.

minimumLayoutSize(Container)

Determines the minimum size of the target container using this grid bag layout.

preferredLayoutSize(Container)

Determines the preferred size of the target container using this grid bag layout.

removeLayoutComponent(Component)

Removes the specified component from this layout.

setConstraints(Component, GridBagConstraints)

Sets the constraints for the specified component in this layout.

toString()

Returns a string representation of this grid bag layout's values.

protected static final int MAXGRIDSIZE

The maximum number of grid positions (both horizontally and vertically) that can be laid out by the grid bag layout.

protected static final int MINSIZE

The smallest grid that can be laid out by the grid bag layout.

protected static final int PREFERREDSIZE

protected Hashtable comptable

protected GridBagConstraints defaultConstraints

protected GridBagLayoutInfo layoutInfo

public int columnWidths[]

public int rowHeights[]

public double columnWeights[]

public double rowWeights[]

public GridBagLayout()

Creates a grid bag layout manager.

public void setConstraints(Component comp,
GridBagConstraints constraints)

Sets the constraints for the specified component in this layout.

Parameters:

comp - the component to be modified.

constraints - the constraints to be applied.

public GridBagConstraints getConstraints(Component comp)

Gets the constraints for the specified component. A copy of the actual GridBagConstraints object is returned.

Parameters:

comp - the component to be queried.

Returns:

the constraint for the specified component in this grid bag layout; a copy of the actual constraint object is returned.

protected GridBagConstraints lookupConstraints(Component comp)

Retrieves the constraints for the specified component. The return value is not a copy, but is the actual GridBagConstraints object used by the layout mechanism.

Parameters:

comp - the component to be queried

Returns:

the contraints for the specified component.

public Point getLayoutOrigin()

Determines the origin of the layout grid. Most applications do not call this method directly.

Returns:

the origin of the cell in the top-left corner of the layout grid.

public int[][] getLayoutDimensions()

Determines column widths and row heights for the layout grid.

Most applications do not call this method directly.

Returns:

an array of two arrays, containing the widths of the layout columns and the heights of the layout rows.

public double[][] getLayoutWeights()

Determines the weights of the layout grid's columns and rows. Weights are used to calculate how much a given column or row stretches beyond its preferred size, if the layout has extra room to fill.

Most applications do not call this method directly.

Returns:

an array of two arrays, representing the horizontal weights of the layout columns and the vertical weights of the layout rows.

public Point location(int x,
                       int y)

Determines which cell in the layout grid contains the point specified by (x, y). Each cell is identified by its column index (ranging from 0 to the number of columns minus 1) and its row index (ranging from 0 to the number of rows minus 1).

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, and as the number of columns if x lies to the right of the layout. 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.

Parameters:

x - the x coordinate of a point.

y - the y coordinate of a point.

Returns:

an ordered pair of indexes that indicate which cell in the layout grid contains the point (x, y).

public void addLayoutComponent(String name,
Component comp)

Adds the specified component with the specified name to the layout.

Parameters:

name - the name of the component.

comp - the component to be added.

public void addLayoutComponent(Component comp,
Object constraints)

Adds the specified component to the layout, using the specified constraint object.

Parameters:

comp - the component to be added.

constraints - an object that determines how the component is added to the layout.

public void removeLayoutComponent(Component comp)

Removes the specified component from this layout.

Most applications do not call this method directly.

Parameters:

comp - the component to be removed.

See Also:

remove, removeAll

public Dimension preferredLayoutSize(Container parent)

Determines the preferred size of the target container using this grid bag layout.

Most applications do not call this method directly.

Parameters:

target - the container in which to do the layout.

See Also:

getPreferredSize

public Dimension minimumLayoutSize(Container parent)

Determines the minimum size of the target container using this grid bag layout.

Most applications do not call this method directly.

Parameters:

target - the container in which to do the layout.

See Also:

doLayout

public Dimension maximumLayoutSize(Container target)

Returns the maximum dimensions for this layout given the components in the specified target container.

Parameters:

target - the component which needs to be laid out

See Also:

Container, minimumLayoutSize, preferredLayoutSize

public float getLayoutAlignmentX(Container parent)

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)

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 void invalidateLayout(Container target)

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

public void layoutContainer(Container parent)

Lays out the specified container using this grid bag layout. This method reshapes components in the specified container in order to satisfy the contraints of this GridBagLayout object.

Most applications do not call this method directly.

Parameters:

parent - the container in which to do the layout.

See Also:

Container, doLayout

public String toString()

Returns a string representation of this grid bag layout's values.

Returns:

a string representation of this grid bag layout.

Overrides:

toString in class Object

protected GridBagLayoutInfo GetLayoutInfo(Container parent,
                                           int sizeflag)

Print the layout constraints. Useful for debugging.

protected void AdjustForGravity(GridBagConstraints constraints,
Rectangle r)

protected Dimension GetMinSize(Container parent,
                                GridBagLayoutInfo info)

protected void ArrangeGrid(Container parent)

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