[Chapter 19] GridBagLayout

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| Chapter 19 java.awt Reference |

# GridBagLayout

## Name

GridBagLayout

##

## Description

The `GridBagLayout` `LayoutManager` provides the means to layout components in a flexible grid-based display model.

## Class Definition

    public class java.awt.GridBagLayout
        extends java.lang.Object
        implements java.awt.LayoutManager2, java.io.Serializable {

      // Protected Constants
      protected static final MAXGRIDSIZE;
      protected static final MINSIZE;
      protected static final PREFERREDSIZE;

      // Variables
      public double columnWeights[];
      public int columnWidths[];
      public int rowHeights[];
      public double rowWeights[];

      // Protected Variables
      protected Hashtable comptable;
      protected GridBagConstraints defaultConstraints;
      protected GridBagLayoutInfo layoutInfo;

      // Constructors
      public GridBagLayout();

      // Instance Methods
      public void addLayoutComponent (Component comp, Object constraints);
      public void addLayoutComponent (String name, Component component);
      public GridBagConstraints getConstraints (Component component);
      public abstract float getLayoutAlignmentX(Container target);
      public abstract float getLayoutAlignmentY(Container target);
      public int[][] getLayoutDimensions();
      public Point getLayoutOrigin();
      public double[][] getLayoutWeights();
      public abstract void invalidateLayout(Container target);
      public void layoutContainer (Container target);
      public Point location (int x, int y);
      public abstract Dimension maximumLayoutSize(Container target);
      public Dimension minimumLayoutSize (Container target);
      public Dimension preferredLayoutSize (Container target);
      public void removeLayoutComponent (Component component);
      public void setConstraints (Component component,
          GridBagConstraints constraints);
      public String toString();

      // Protected Instance Methods
      protected void AdjustForGravity (GridBagConstraints constraints,
          Rectangle r);
      protected void ArrangeGrid (Container target);
      protected GridBagLayoutInfo GetLayoutInfo (Container target,
          int sizeFlag);
      protected Dimension GetMinSize (Container target,
          GridBagLayoutInfo info);
      protected GridBagConstraints lookupConstraints (Component comp);
    }

## Protected Constants

### MAXGRIDSIZE

#### protected static final MAXGRIDSIZE

Maximum number of rows and columns within container managed by `GridBagLayout`.

### MINSIZE

#### protected static final MINSIZE

Used for internal sizing purposes.

### PREFERREDSIZE

#### protected static final PREFERREDSIZE

Used for internal sizing purposes.

## Variables

### columnWeights

#### public double[] columnWeights

The `weightx` values of the components in the row with the most elements.

### columnWidths

#### public int[] columnWidths

The `width` values of the components in the row with the most elements.

### rowHeights

#### public int[] rowHeights

The `height` values of the components in the column with the most elements.

### rowWeights

#### public double[] rowWeights

The `weighty` values of the components in the column with the most elements.

## Protected Variables

### comptable

#### protected Hashtable comptable

Internal table to manage components.

### defaultConstraints

#### protected GridBagConstraints defaultConstraints

Constraints to use for `Component`s that have none.

### layoutInfo

#### protected GridBagLayoutInfo layoutInfo

Internal information about the `GridBagLayout`.

## Constructors

### GridBagLayout

#### public GridBagLayout()

Description

  Constructs a `GridBagLayout` object.

## Instance Methods

### addLayoutComponent

#### public void addLayoutComponent (Component comp, Object constraints)

Parameters

  comp

    The component being added.

  constraints

    An object describing the constraints on this component.

Implements

  `LayoutManager2.addLayoutComponent()`

Description

  Adds the component `comp` to container subject to the given `constraints`. This is a more generalized version of `addLayoutComponent(String, Component)`. It corresponds to `java.awt.Container's add(Component, Object)`.

#### public void addLayoutComponent (String name, Component component)

Parameters

  name

    Name of component to add.

  component

    Actual component being added.

Implements

  `LayoutManager.addLayoutComponent()`

Description

  Does nothing.

### getConstraints

#### public GridBagConstraints getConstraints (Component component)

Parameters

  component

    Component whose constraints are desired

Returns

  `GridBagConstraints` for component requested.

### getLayoutAlignmentX

#### public abstract float getLayoutAlignmentX (Container target)

Parameters

  target

    The container to inspect.

Returns

  The value .5 for all containers.

Description

  This method returns the preferred alignment of the given container `target`. A return value of 0 is left aligned, .5 is centered, and 1 is right aligned.

### getLayoutAlignmentY

#### public abstract float getLayoutAlignmentY (Container target)

Parameters

  target

    The container to inspect.

Returns

  The value .5 for all containers.

Description

  This method returns the preferred alignment of the given container `target`. A return value of 0 is top aligned, .5 is centered, and 1 is bottom aligned.

### getLayoutDimensions

#### public int[][] getLayoutDimensions()

Returns

  Returns two single dimension arrays as a multi-dimensional array. Index 0 is an array of widths (`columnWidths` instance variable), while index 1 is an array of heights (`rowHeights` instance variable).

### getLayoutOrigin

#### public Point getLayoutOrigin()

Returns

  Returns the origin of the components within the `Container` whose `LayoutManager` is `GridBagLayout`.

### getLayoutWeights

#### public double[][] getLayoutWeights()

Returns

  Returns two single dimension arrays as a multi-dimensional array. Index 0 is an array of columns weights (`columnWeights` instance variable), while index 1 is an array of row weights (`rowWeights` instance variable).

### invalidateLayout

#### public abstract void invalidateLayout (Container target)

Parameters

  target

    The container to invalidate.

Description

  Does nothing.

### layoutContainer

#### public void layoutContainer (Container target)

Parameters

  target

    The container that needs to be redrawn.

Implements

  `LayoutManager.layoutContainer()`

Description

  Draws components contained within `target`.

### location

#### public Point location (int x, int y)

Parameters

  x

    The x coordinate of the grid position to find.

  y

    The y coordinate of the grid position to find.

Returns

  Returns the grid element under the location provided at position (`x`, `y`) in pixels. Note that the returned Point uses the `GridBagLayout`'s grid for its coordinate space.

Description

  Locates the grid position in the `Container` under the given location.

### maximumLayoutSize

#### public abstract Dimension maximumLayoutSize (Container target)

Parameters

  target

    The container to inspect.

Returns

  A `Dimension` whose horizontal and vertical components are `Integer.MAX_VALUE`.

Description

  For `GridBagLayout`, a maximal `Dimension` is always returned.

### minimumLayoutSize

#### public Dimension minimumLayoutSize (Container target)

Parameters

  target

    The container whose size needs to be calculated.

Returns

  Minimum `Dimension` of container target.

Implements

  `LayoutManager.minimumLayoutSize()`

Description

  Calculates minimum size of `target` container.

### preferredLayoutSize

#### public Dimension preferredLayoutSize (Container target)

Parameters

  target

    The container whose size needs to be calculated.

Returns

  Preferred `Dimension` of container target

Implements

  `LayoutManager.preferredLayoutSize()`

Description

  Calculates preferred size of `target` container.

### removeLayoutComponent

#### public void removeLayoutComponent (Component component)

Parameters

  component

    Component to stop tracking.

Implements

  `LayoutManager.removeLayoutComponent()`

Description

  Does nothing.

### setConstraints

#### public void setConstraints (Component component, GridBagConstraints constraints)

Parameters

  component

    Component to set constraints for

  constraints

    Constraints for component

Description

  Changes the `GridBagConstraints` on `component` to those provided.

### toString

#### public String toString()

Returns

  A string representation of the `GridBagLayout` object.

Overrides

  `Object.toString()`

## Protected Instance Methods

### AdjustForGravity

#### protected void AdjustForGravity (GridBagConstraints constraints, Rectangle r)

Parameters

  constraints

    Constraints to use for adjustment of Rectangle.

  r

    Rectangular area that needs to be adjusted.

Description

  Helper routine for laying out a cell of the grid. The routine adjusts the values for `r` based upon the `constraints`.

### ArrangeGrid

#### protected void ArrangeGrid (Container target)

Parameters

  target

    `Container` to layout.

Description

  Helper routine that does the actual arrangement of components in `target`.

### GetLayoutInfo

#### protected GridBagLayoutInfo GetLayoutInfo (Container target, int sizeFlag)

Parameters

  target

    `Container` to get information about.

  sizeFlag

    One of the constants `MINSIZE` or `PREFERREDSIZE`.

Returns

  Returns an internal class used to help size the container.

### GetMinSize

#### protected Dimension GetMinSize (Container target, GridBagLayoutInfo info)

Parameters

  target

    `Container` to calculate size.

  info

    Specifics about the container's constraints.

Returns

  Minimum `Dimension` of container target based on info.

Description

  Helper routine for calculating size of container.

### lookupConstraints

#### protected GridBagConstraints lookupConstraints (Component comp)

Parameters

  comp

    `Component` in question.

Returns

  A reference to the `GridBagConstraints` object for this component.

Description

  Helper routine for calculating size of container.

## See Also

`Component`, `Container`, `Dimension`, `GridBagConstraints`, `Hashtable`, `LayoutManager`, `LayoutManager2`, `Object`, `Point`, `Rectangle`, `String`

GridBagConstraints |  | GridLayout