java.awt
Class GridBagLayout

java.lang.Object
  java.awt.GridBagLayout

All Implemented Interfaces:

LayoutManager, LayoutManager2, Serializable

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 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:

GridBagConstraints.gridx, GridBagConstraints.gridy

Specifies the cell containing the leading corner of the component's display area, where the cell at the origin of the grid has address gridx = 0, gridy = 0. For horizontal left-to-right layout, a component's leading corner is its upper left. For horizontal right-to-left layout, a component's leading corner is its upper right. Use GridBagConstraints.RELATIVE (the default value) to specify that the component be placed immediately following (along the x axis for gridx or the y axis for gridy) the component that was added to the container just before this component was added.

GridBagConstraints.gridwidth, GridBagConstraints.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's display area will be from gridx to the last cell in the row (for gridwidth) or from gridy to the last cell in the column (for gridheight). Use GridBagConstraints.RELATIVE to specify that the component's display area will be from gridx to the next to the last cell in its row (for gridwidth or from gridy to the next to the last cell in its column (for gridheight).

GridBagConstraints.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).

GridBagConstraints.ipadx, GridBagConstraints.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 pixels. Similarly, the height of the component will be at least the minimum height plus ipady pixels.

GridBagConstraints.insets

Specifies the component's external padding, the minimum amount of space between the component and the edges of its display area.

GridBagConstraints.anchor

Used when the component is smaller than its display area to determine where (within the display area) to place the component. There are two kinds of possible values: relative and absolute. Relative values are interpreted relative to the container's ComponentOrientation property while absolute values are not. Valid values are:

Absolute Values	Relative Values
GridBagConstraints.NORTH GridBagConstraints.SOUTH GridBagConstraints.WEST GridBagConstraints.EAST GridBagConstraints.NORTHWEST GridBagConstraints.NORTHEAST GridBagConstraints.SOUTHWEST GridBagConstraints.SOUTHEAST GridBagConstraints.CENTER (the default)	GridBagConstraints.PAGE_START GridBagConstraints.PAGE_END GridBagConstraints.LINE_START GridBagConstraints.LINE_END GridBagConstraints.FIRST_LINE_START GridBagConstraints.FIRST_LINE_END GridBagConstraints.LAST_LINE_START GridBagConstraints.LAST_LINE_END

GridBagConstraints.weightx, GridBagConstraints.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 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.

Figure 1: Horizontal, Left-to-Right	Figure 2: Horizontal, Right-to-Left

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("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();
     }
 }
 

Since:

JDK1.0

See Also:

GridBagConstraints, ComponentOrientation, Serialized Form

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
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

MAXGRIDSIZE

protected static final int MAXGRIDSIZE

See Also:

Constant Field Values

MINSIZE

protected static final int MINSIZE

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

See Also:

Constant Field Values

PREFERREDSIZE

protected static final int PREFERREDSIZE

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

See Also:

Constant Field Values

comptable

protected Hashtable<Component,GridBagConstraints> comptable

This hashtable maintains the association between a component and its gridbag constraints. The Keys in comptable are the components and the values are the instances of GridBagConstraints.

See Also:

GridBagConstraints

defaultConstraints

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.

See Also:

getConstraints(Component), setConstraints(Component, GridBagConstraints), lookupConstraints(Component)

layoutInfo

protected java.awt.GridBagLayoutInfo layoutInfo

This field holds the layout information for the gridbag. The information in this field is based on the most recent validation of the gridbag. If layoutInfo is null this indicates that there are no components in the gridbag or if there are components, they have not yet been validated.

See Also:

getLayoutInfo(Container, int)

columnWidths

public int[] columnWidths

This field holds the overrides to the column minimum width. If this field is non-null the values are applied to the gridbag after all of the minimum columns widths have been calculated. If columnWidths has more elements than the number of columns, columns are added to the gridbag to match the number of elements in columnWidth.

See Also:

getLayoutDimensions()

rowHeights

public int[] rowHeights

This field holds the overrides to the row minimum heights. If this field is non-null the values are applied to the gridbag after all of the minimum row heights have been calculated. If rowHeights has more elements than the number of rows, rowa are added to the gridbag to match the number of elements in rowHeights.

See Also:

getLayoutDimensions()

columnWeights

public double[] columnWeights

This field holds the overrides to the column weights. If this field is non-null the values are applied to the gridbag after all of the columns weights have been calculated. If columnWeights[i] > weight for column i, then column i is assigned the weight in columnWeights[i]. If columnWeights has more elements than the number of columns, the excess elements are ignored - they do not cause more columns to be created.

rowWeights

public double[] rowWeights

This field holds the overrides to the row weights. If this field is non-null the values are applied to the gridbag after all of the rows weights have been calculated. If rowWeights[i] > weight for row i, then row i is assigned the weight in rowWeights[i]. If rowWeights has more elements than the number of rows, the excess elements are ignored - they do not cause more rows to be created.

Constructor Detail

GridBagLayout

public GridBagLayout()

Creates a grid bag layout manager.

Method Detail

setConstraints

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

getConstraints

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

lookupConstraints

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.

If comp is not in the GridBagLayout, a set of default GridBagConstraints are returned. A comp value of null is invalid and returns null.

Parameters:

comp - the component to be queried

Returns:

the contraints for the specified component

getLayoutOrigin

public Point getLayoutOrigin()

Determines the origin of the layout area, in the graphics coordinate space of the target container. This value represents the pixel coordinates of the top-left corner of the layout area regardless of the ComponentOrientation value of the container. This is distinct from the grid origin given by the cell coordinates (0,0). Most applications do not call this method directly.

Returns:

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

Since:

JDK1.1

See Also:

ComponentOrientation

getLayoutDimensions

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

Since:

JDK1.1

getLayoutWeights

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

Since:

JDK1.1

location

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 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.

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).

Since:

JDK1.1

See Also:

ComponentOrientation

addLayoutComponent

public void addLayoutComponent(String name,
                               Component comp)

Has no effect, since this layout manager does not use a per-component string.

Specified by:

addLayoutComponent in interface LayoutManager

Parameters:

name - the string to be associated with the component

comp - the component to be added

addLayoutComponent

public void addLayoutComponent(Component comp,
                               Object constraints)

Adds the specified component to the layout, using the specified constraints object. Note that constraints are mutable and are, therefore, cloned when cached.

Specified by:

addLayoutComponent in interface LayoutManager2

Parameters:

comp - the component to be added

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

Throws:

IllegalArgumentException - if constraints is not a GridBagConstraint

removeLayoutComponent

public void removeLayoutComponent(Component comp)

Removes the specified component from this layout.

Most applications do not call this method directly.

Specified by:

removeLayoutComponent in interface LayoutManager

Parameters:

comp - the component to be removed.

See Also:

Container.remove(java.awt.Component), Container.removeAll()

preferredLayoutSize

public Dimension preferredLayoutSize(Container parent)

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

Most applications do not call this method directly.

Specified by:

preferredLayoutSize in interface LayoutManager

Parameters:

parent - the container in which to do the layout

Returns:

the preferred size of the parent container

See Also:

Container.getPreferredSize()

minimumLayoutSize

public Dimension minimumLayoutSize(Container parent)

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

Most applications do not call this method directly.

Specified by:

minimumLayoutSize in interface LayoutManager

Parameters:

parent - the container in which to do the layout

Returns:

the minimum size of the parent container

See Also:

Container.doLayout()

maximumLayoutSize

public Dimension maximumLayoutSize(Container target)

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

Specified by:

maximumLayoutSize in interface LayoutManager2

Parameters:

target - the container which needs to be laid out

Returns:

the maximum dimensions for this layout

See Also:

Container, minimumLayoutSize(Container), preferredLayoutSize(Container)

getLayoutAlignmentX

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.

Specified by:

getLayoutAlignmentX in interface LayoutManager2

Returns:

the value 0.5f to indicate centered

getLayoutAlignmentY

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.

Specified by:

getLayoutAlignmentY in interface LayoutManager2

Returns:

the value 0.5f to indicate centered

invalidateLayout

public void invalidateLayout(Container target)

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

Specified by:

invalidateLayout in interface LayoutManager2

layoutContainer

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.

Specified by:

layoutContainer in interface LayoutManager

Parameters:

parent - the container in which to do the layout

See Also:

Container, Container.doLayout()

toString

public String toString()

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

Overrides:

toString in class Object

Returns:

a string representation of this grid bag layout.

getLayoutInfo

protected java.awt.GridBagLayoutInfo getLayoutInfo(Container parent,
                                                   int sizeflag)

Fills in an instance of GridBagLayoutInfo for the current set of managed children. This requires three passes through the set of children:

1. Figure out the dimensions of the layout grid.
2. Determine which cells the components occupy.
3. Distribute the weights and min sizes amoung the rows/columns.

This also caches the minsizes for all the children when they are first encountered (so subsequent loops don't need to ask again).

This method should only be used internally by GridBagLayout.

Parameters:

parent - the layout container

sizeflag - either PREFERREDSIZE or MINSIZE

Returns:

the GridBagLayoutInfo for the set of children

Since:

1.4

GetLayoutInfo

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. This method is the same as getLayoutInfo; refer to getLayoutInfo for details on parameters and return value.

adjustForGravity

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. This method should only be used internally by GridBagLayout.

Parameters:

constraints - the constraints to be applied

r - the Rectangle to be adjusted

Since:

1.4

AdjustForGravity

protected void AdjustForGravity(GridBagConstraints constraints,
                                Rectangle r)

This method is obsolete and supplied for backwards compatability only; new code should call adjustForGravity instead. This method is the same as adjustForGravity; refer to adjustForGravity for details on parameters.

getMinSize

protected Dimension getMinSize(Container parent,
                               java.awt.GridBagLayoutInfo info)

Figures out the minimum size of the master based on the information from getLayoutInfo. This method should only be used internally by GridBagLayout.

Parameters:

parent - the layout container

info - the layout info for this parent

Returns:

a Dimension object containing the minimum size

Since:

1.4

GetMinSize

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. This method is the same as getMinSize; refer to getMinSize for details on parameters and return value.

arrangeGrid

protected void arrangeGrid(Container parent)

Lays out the grid. This method should only be used internally by GridBagLayout.

Parameters:

parent - the layout container

Since:

1.4

ArrangeGrid

protected void ArrangeGrid(Container parent)

This method is obsolete and supplied for backwards compatability only; new code should call arrangeGrid instead. This method is the same as arrangeGrid; refer to arrangeGrid for details on the parameter.