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# Class java.awt.GridBagLayout

    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:

- 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.

##

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.

MINSIZE

     protected static final int MINSIZE

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

PREFERREDSIZE

     protected static final int PREFERREDSIZE

comptable

     protected Hashtable comptable

defaultConstraints

     protected GridBagConstraints defaultConstraints

layoutInfo

     protected GridBagLayoutInfo layoutInfo

columnWidths

     public int columnWidths[]

rowHeights

     public int rowHeights[]

columnWeights

     public double columnWeights[]

rowWeights

     public double rowWeights[]

##

GridBagLayout

     public GridBagLayout()

  Creates a grid bag layout manager.

##

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 grid. Most applications do not call this method directly.

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

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.

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.

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).

addLayoutComponent

     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.

addLayoutComponent

     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.

removeLayoutComponent

     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

preferredLayoutSize

     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

minimumLayoutSize

     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

maximumLayoutSize

     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

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.

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.

invalidateLayout

     public void invalidateLayout(Container target)

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

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.

  Parameters:
    parent - the container in which to do the layout.
  See Also:
    Container, doLayout

toString

     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

GetLayoutInfo

     protected GridBagLayoutInfo GetLayoutInfo(Container parent,
                                               int sizeflag)

  Print the layout constraints. Useful for debugging.

AdjustForGravity

     protected void AdjustForGravity(GridBagConstraints constraints,
                                     Rectangle r)

GetMinSize

     protected Dimension GetMinSize(Container parent,
                                    GridBagLayoutInfo info)

ArrangeGrid

     protected void ArrangeGrid(Container parent)

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