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, horizontally or along their baseline 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
Specifies where the component should be positioned in its display area. There are three kinds of possible values: absolute, orientation-relative, and baseline-relative. Orientation relative values are interpreted relative to the container's ComponentOrientation property while absolute values are not. Baseline relative values are calculated relative to the baseline. Valid values are:
  • Absolute Values:
    • GridBagConstraints.NORTH
    • GridBagConstraints.SOUTH
    • GridBagConstraints.WEST
    • GridBagConstraints.EAST
    • GridBagConstraints.NORTHWEST
    • GridBagConstraints.NORTHEAST
    • GridBagConstraints.SOUTHWEST
    • GridBagConstraints.SOUTHEAST
    • GridBagConstraints.CENTER (the default)
  • Orientation Relative Values:
    • 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
  • Baseline Relative Values:
    • GridBagConstraints.BASELINE
    • GridBagConstraints.BASELINE_LEADING
    • GridBagConstraints.BASELINE_TRAILING
    • GridBagConstraints.ABOVE_BASELINE
    • GridBagConstraints.ABOVE_BASELINE_LEADING
    • GridBagConstraints.ABOVE_BASELINE_TRAILING
    • GridBagConstraints.BELOW_BASELINE
    • GridBagConstraints.BELOW_BASELINE_LEADING
    • GridBagConstraints.BELOW_BASELINE_TRAILING
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.

Each row may have a baseline; the baseline is determined by the components in that row that have a valid baseline and are aligned along the baseline (the component's anchor value is one of BASELINE, BASELINE_LEADING or BASELINE_TRAILING). If none of the components in the row has a valid baseline, the row does not have a baseline.

If a component spans rows it is aligned either to the baseline of the start row (if the baseline-resize behavior is CONSTANT_ASCENT) or the end row (if the baseline-resize behavior is CONSTANT_DESCENT). The row that the component is aligned to is called the prevailing row.

The following figure shows a baseline layout and includes a component that spans rows:

The following text describes this graphic (Figure 1).

This layout consists of three components:
  • A panel that starts in row 0 and ends in row 1. The panel has a baseline-resize behavior of CONSTANT_DESCENT and has an anchor of BASELINE. As the baseline-resize behavior is CONSTANT_DESCENT the prevailing row for the panel is row 1.
  • Two buttons, each with a baseline-resize behavior of CENTER_OFFSET and an anchor of BASELINE.
Because the second button and the panel share the same prevailing row, they are both aligned along their baseline.

Components positioned using one of the baseline-relative values resize differently than when positioned using an absolute or orientation-relative value. How components change is dictated by how the baseline of the prevailing row changes. The baseline is anchored to the bottom of the display area if any components with the same prevailing row have a baseline-resize behavior of CONSTANT_DESCENT, otherwise the baseline is anchored to the top of the display area. The following rules dictate the resize behavior:

  • Resizable components positioned above the baseline can only grow as tall as the baseline. For example, if the baseline is at 100 and anchored at the top, a resizable component positioned above the baseline can never grow more than 100 units.
  • Similarly, resizable components positioned below the baseline can only grow as high as the difference between the display height and the baseline.
  • Resizable components positioned on the baseline with a baseline-resize behavior of OTHER are only resized if the baseline at the resized size fits within the display area. If the baseline is such that it does not fit within the display area the component is not resized.
  • Components positioned on the baseline that do not have a baseline-resize behavior of OTHER can only grow as tall as display height - baseline + baseline of component.
If you position a component along the baseline, but the component does not have a valid baseline, it will be vertically centered in its space. Similarly if you have positioned a component relative to the baseline and none of the components in the row have a valid baseline the component is vertically centered.

The following figures show ten components (all buttons) managed by a grid bag layout. Figure 2 shows the layout for a horizontal, left-to-right container and Figure 3 shows the layout for a horizontal, right-to-left container.

The preceding text describes this graphic (Figure 2).

Figure 2: Horizontal, Left-to-Right

The preceding text describes this graphic (Figure 3).

Figure 3: 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:
1.0
See Also:

  • Field Details

    • MAXGRIDSIZE

      protected static final int MAXGRIDSIZE
      This field is no longer used to reserve arrays and kept for backward compatibility. Previously, this was the maximum number of grid positions (both horizontal and vertical) that could be laid out by the grid bag layout. Current implementation doesn't impose any limits on the size of a grid.
      See Also:

    • MINSIZE

      protected static final int MINSIZE
      The smallest grid that can be laid out by the grid bag layout.
      See Also:

    • PREFERREDSIZE

      protected static final int PREFERREDSIZE
      The preferred grid size that can be laid out by the grid bag layout.
      See Also:

    • 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:

    • 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:

    • layoutInfo

      protected 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:

    • 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:

    • 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, rows are added to the gridbag to match the number of elements in rowHeights.
      See Also:

    • 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 Details

    • GridBagLayout

      public GridBagLayout()
      Creates a grid bag layout manager.

  • Method Details

    • 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 constraints 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:
      1.1
      See Also:

    • 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:
      1.1

    • 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:
      1.1

    • 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:
      1.1
      See Also:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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
      Parameters:
      parent - the target container
      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
      Parameters:
      parent - the target container
      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
      Parameters:
      target - the target container

    • 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 constraints 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:

    • 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 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 among 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 GridBagLayoutInfo GetLayoutInfo(Container parent, int sizeflag)
      This method is obsolete and supplied for backwards compatibility only; new code should call getLayoutInfo instead. Fills in an instance of GridBagLayoutInfo for the current set of managed children. This method is the same as getLayoutInfo; refer to getLayoutInfo description for details.
      Parameters:
      parent - the layout container
      sizeflag - either PREFERREDSIZE or MINSIZE
      Returns:
      the GridBagLayoutInfo for the set of children

    • 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)
      Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads.

      This method is obsolete and supplied for backwards compatibility only; new code should call adjustForGravity instead. This method is the same as adjustForGravity

      Parameters:
      constraints - the constraints to be applied
      r - the Rectangle to be adjusted

    • getMinSize

      protected Dimension getMinSize(Container parent, GridBagLayoutInfo info)
      Figures out the minimum size of the parent 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, GridBagLayoutInfo info)
      This method is obsolete and supplied for backwards compatibility only; new code should call getMinSize instead. This method is the same as getMinSize
      Parameters:
      parent - the layout container
      info - the layout info for this parent
      Returns:
      a Dimension object containing the minimum size

    • 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 compatibility only; new code should call arrangeGrid instead. This method is the same as arrangeGrid
      Parameters:
      parent - the layout container