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java.awt
Class GridBagLayout


java.lang.Object
  extended by 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 component be from gridx to the last cell one in the its 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 component be from gridx to the next to the last cell one in its row (for gridwidth 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 * 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. 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.

    The preceeding text describes this graphic (Figure 1). The preceeding text describes this graphic (Figure 2).
    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:

    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("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
    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 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
              As of 1.5, this field is no longer used.
    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
    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
              Has no effect, since this layout manager does not use a per-component string.           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.
    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
              Figures out the minimum size of the master based on the information from getLayoutInfo. 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
    As of 1.5, this field is no longer used. Previously, this was the The maximum number of grid positions (both horizontal horizontally and vertical) vertically) that could 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)

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

    Specified by:
    addLayoutComponent in interface LayoutManager
    Parameters:
    name - the string to be associated with 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.

    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. getLayoutInfo().

    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.