GridBagLayout (ocap 1.2 API)

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.

Grid coordinate (0,0) is in the upper left corner of the container with x increasing to the right 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 at the upper left of the component's display area, where the cell at the origin of the grid has address gridx = 0, gridy = 0. 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 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).
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 * 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.
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.
Valid values are:
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 figure shows ten components (all buttons) managed by a grid bag layout:

The preceeding text describes this graphic (Figure 1).

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

Note: The following code example includes classes that do not appear in this specification. Their inclusion is purely to serve as a demonstration.

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();
     }
 }

Since:: JDK1.0
Version:: 1.5, 16 Nov 1995
Author:: Doug Stein
See Also:: GridBagConstraints, Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`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`	`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 static int`	`MAXGRIDSIZE` The maximum number of grid positions (both horizontally and vertically) that can be laid out by the grid bag layout.
`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

Constructors
Constructor and Description

GridBagLayout()
Creates a grid bag layout manager.

Constructors
Constructor and Description
`GridBagLayout()` Creates a grid bag layout manager.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`addLayoutComponent(Component comp, Object constraints)` Adds the specified component to the layout, using the specified `constraints` object.
`void`	`addLayoutComponent(String name, Component comp)` Adds the specified component with the specified name to the layout.
`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.
`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.
`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
```
    The maximum number of grid positions (both horizontally and vertically) that can be laid out by the grid bag layout.
    
    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 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)
  - 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.
    
    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 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
  - 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, 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).
    Since:
    
    JDK1.1
  - addLayoutComponent
```
public void addLayoutComponent(String name,
                      Component comp)
```
    Adds the specified component with the specified name to the layout.
    
    Specified by:
    
    addLayoutComponent in interface LayoutManager
    
    Parameters:
    name - the name of 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.
  - 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.
    
    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.
  - arrangeGrid
```
protected void arrangeGrid(Container parent)
```
    Lays out the grid.
    
    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.

Class GridBagLayout

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

MAXGRIDSIZE

MINSIZE

PREFERREDSIZE

comptable

defaultConstraints

columnWidths

rowHeights

columnWeights

rowWeights

Constructor Detail

GridBagLayout

Method Detail

setConstraints

getConstraints

lookupConstraints

getLayoutOrigin

getLayoutDimensions

getLayoutWeights

location

addLayoutComponent

addLayoutComponent

removeLayoutComponent

preferredLayoutSize

minimumLayoutSize

maximumLayoutSize

getLayoutAlignmentX

getLayoutAlignmentY

invalidateLayout

layoutContainer

toString

adjustForGravity

AdjustForGravity

arrangeGrid

ArrangeGrid