- All Implemented Interfaces:
LayoutManager,LayoutManager2,Serializable
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. UseGridBagConstraints.RELATIVE(the default value) to specify that the component be placed immediately following (along the x axis forgridxor the y axis forgridy) 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 (forgridheight) in the component's display area. The default value is 1. UseGridBagConstraints.REMAINDERto specify that the component's display area will be fromgridxto the last cell in the row (forgridwidth) or fromgridyto the last cell in the column (forgridheight). UseGridBagConstraints.RELATIVEto specify that the component's display area will be fromgridxto the next to the last cell in its row (forgridwidth) or fromgridyto the next to the last cell in its column (forgridheight). 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), andGridBagConstraints.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
ipadxpixels. Similarly, the height of the component will be at least the minimum height plusipadypixels. 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
ComponentOrientationproperty while absolute values are not. Baseline relative values are calculated relative to the baseline. Valid values are:- Absolute Values:
GridBagConstraints.NORTHGridBagConstraints.SOUTHGridBagConstraints.WESTGridBagConstraints.EASTGridBagConstraints.NORTHWESTGridBagConstraints.NORTHEASTGridBagConstraints.SOUTHWESTGridBagConstraints.SOUTHEASTGridBagConstraints.CENTER(the default)
- Orientation Relative Values:
GridBagConstraints.PAGE_STARTGridBagConstraints.PAGE_ENDGridBagConstraints.LINE_STARTGridBagConstraints.LINE_ENDGridBagConstraints.FIRST_LINE_STARTGridBagConstraints.FIRST_LINE_ENDGridBagConstraints.LAST_LINE_STARTGridBagConstraints.LAST_LINE_END
- Baseline Relative Values:
GridBagConstraints.BASELINEGridBagConstraints.BASELINE_LEADINGGridBagConstraints.BASELINE_TRAILINGGridBagConstraints.ABOVE_BASELINEGridBagConstraints.ABOVE_BASELINE_LEADINGGridBagConstraints.ABOVE_BASELINE_TRAILINGGridBagConstraints.BELOW_BASELINEGridBagConstraints.BELOW_BASELINE_LEADINGGridBagConstraints.BELOW_BASELINE_TRAILING
- Absolute Values:
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), theGridBagLayoutobject 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:
- A panel that starts in row 0 and ends in row 1. The panel
has a baseline-resize behavior of
CONSTANT_DESCENTand has an anchor ofBASELINE. As the baseline-resize behavior isCONSTANT_DESCENTthe prevailing row for the panel is row 1. - Two buttons, each with a baseline-resize behavior of
CENTER_OFFSETand an anchor ofBASELINE.
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
OTHERare 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
OTHERcan only grow as tall asdisplay height - baseline + baseline of component.
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.
Figure 2: Horizontal, Left-to-Right
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:
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Field Summary
FieldsModifier and TypeFieldDescriptiondouble[]This field holds the overrides to the column weights.int[]This field holds the overrides to the column minimum width.protected Hashtable<Component, GridBagConstraints> This hashtable maintains the association between a component and its gridbag constraints.protected GridBagConstraintsThis 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 thedefaultConstraints.protected GridBagLayoutInfoThis field holds the layout information for the gridbag.protected static final intThis field is no longer used to reserve arrays and kept for backward compatibility.protected static final intThe smallest grid that can be laid out by the grid bag layout.protected static final intThe preferred grid size that can be laid out by the grid bag layout.int[]This field holds the overrides to the row minimum heights.double[]This field holds the overrides to the row weights. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoidaddLayoutComponent(Component comp, Object constraints) Adds the specified component to the layout, using the specifiedconstraintsobject.voidaddLayoutComponent(String name, Component comp) Has no effect, since this layout manager does not use a per-component string.protected voidadjustForGravity(GridBagConstraints constraints, Rectangle r) Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads.protected voidAdjustForGravity(GridBagConstraints constraints, Rectangle r) Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads.protected voidarrangeGrid(Container parent) Lays out the grid.protected voidArrangeGrid(Container parent) This method is obsolete and supplied for backwards compatibility only; new code should callarrangeGridinstead.getConstraints(Component comp) Gets the constraints for the specified component.floatgetLayoutAlignmentX(Container parent) Returns the alignment along the x axis.floatgetLayoutAlignmentY(Container parent) Returns the alignment along the y axis.int[][]Determines column widths and row heights for the layout grid.protected GridBagLayoutInfogetLayoutInfo(Container parent, int sizeflag) Fills in an instance ofGridBagLayoutInfofor the current set of managed children.protected GridBagLayoutInfoGetLayoutInfo(Container parent, int sizeflag) This method is obsolete and supplied for backwards compatibility only; new code should callgetLayoutInfoinstead.Determines the origin of the layout area, in the graphics coordinate space of the target container.double[][]Determines the weights of the layout grid's columns and rows.protected DimensiongetMinSize(Container parent, GridBagLayoutInfo info) Figures out the minimum size of the parent based on the information fromgetLayoutInfo.protected DimensionGetMinSize(Container parent, GridBagLayoutInfo info) This method is obsolete and supplied for backwards compatibility only; new code should callgetMinSizeinstead.voidinvalidateLayout(Container target) Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.voidlayoutContainer(Container parent) Lays out the specified container using this grid bag layout.location(int x, int y) Determines which cell in the layout grid contains the point specified by(x, y).protected GridBagConstraintslookupConstraints(Component comp) Retrieves the constraints for the specified component.maximumLayoutSize(Container target) Returns the maximum dimensions for this layout given the components in the specified target container.minimumLayoutSize(Container parent) Determines the minimum size of theparentcontainer using this grid bag layout.preferredLayoutSize(Container parent) Determines the preferred size of theparentcontainer using this grid bag layout.voidRemoves the specified component from this layout.voidsetConstraints(Component comp, GridBagConstraints constraints) Sets the constraints for the specified component in this layout.toString()Returns a string representation of this grid bag layout's values.
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Field Details
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MAXGRIDSIZE
protected static final int MAXGRIDSIZEThis 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:
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MINSIZE
protected static final int MINSIZEThe smallest grid that can be laid out by the grid bag layout.- See Also:
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PREFERREDSIZE
protected static final int PREFERREDSIZEThe preferred grid size that can be laid out by the grid bag layout.- See Also:
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comptable
This hashtable maintains the association between a component and its gridbag constraints. The Keys incomptableare the components and the values are the instances ofGridBagConstraints.- See Also:
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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 thedefaultConstraints.- See Also:
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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. IflayoutInfoisnullthis indicates that there are no components in the gridbag or if there are components, they have not yet been validated.- See Also:
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columnWidths
public int[] columnWidthsThis field holds the overrides to the column minimum width. If this field is non-nullthe 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:
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rowHeights
public int[] rowHeightsThis field holds the overrides to the row minimum heights. If this field is non-nullthe values are applied to the gridbag after all of the minimum row heights have been calculated. IfrowHeightshas more elements than the number of rows, rows are added to the gridbag to match the number of elements inrowHeights.- See Also:
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columnWeights
public double[] columnWeightsThis field holds the overrides to the column weights. If this field is non-nullthe values are applied to the gridbag after all of the columns weights have been calculated. IfcolumnWeights[i] >weight for column i, then column i is assigned the weight incolumnWeights[i]. IfcolumnWeightshas more elements than the number of columns, the excess elements are ignored - they do not cause more columns to be created. -
rowWeights
public double[] rowWeightsThis field holds the overrides to the row weights. If this field is non-nullthe values are applied to the gridbag after all of the rows weights have been calculated. IfrowWeights[i] >weight for row i, then row i is assigned the weight inrowWeights[i]. IfrowWeightshas more elements than the number of rows, the excess elements are ignored - they do not cause more rows to be created.
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Constructor Details
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GridBagLayout
public GridBagLayout()Creates a grid bag layout manager.
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Method Details
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setConstraints
Sets the constraints for the specified component in this layout.- Parameters:
comp- the component to be modifiedconstraints- the constraints to be applied
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getConstraints
Gets the constraints for the specified component. A copy of the actualGridBagConstraintsobject 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
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lookupConstraints
Retrieves the constraints for the specified component. The return value is not a copy, but is the actualGridBagConstraintsobject used by the layout mechanism.If
compis not in theGridBagLayout, a set of defaultGridBagConstraintsare returned. Acompvalue ofnullis invalid and returnsnull.- Parameters:
comp- the component to be queried- Returns:
- the constraints for the specified component
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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 theComponentOrientationvalue 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:
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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
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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
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location
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 ifxlies 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 ifxlies 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 ifylies above the layout, and as the number of rows ifylies below the layout. The orientation of a container is determined by itsComponentOrientationproperty.- Parameters:
x- the x coordinate of a pointy- 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:
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addLayoutComponent
Has no effect, since this layout manager does not use a per-component string.- Specified by:
addLayoutComponentin interfaceLayoutManager- Parameters:
name- the string to be associated with the componentcomp- the component to be added
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addLayoutComponent
Adds the specified component to the layout, using the specifiedconstraintsobject. Note that constraints are mutable and are, therefore, cloned when cached.- Specified by:
addLayoutComponentin interfaceLayoutManager2- Parameters:
comp- the component to be addedconstraints- an object that determines how the component is added to the layout- Throws:
IllegalArgumentException- ifconstraintsis not aGridBagConstraint
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removeLayoutComponent
Removes the specified component from this layout.Most applications do not call this method directly.
- Specified by:
removeLayoutComponentin interfaceLayoutManager- Parameters:
comp- the component to be removed.- See Also:
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preferredLayoutSize
Determines the preferred size of theparentcontainer using this grid bag layout.Most applications do not call this method directly.
- Specified by:
preferredLayoutSizein interfaceLayoutManager- Parameters:
parent- the container in which to do the layout- Returns:
- the preferred size of the
parentcontainer - See Also:
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minimumLayoutSize
Determines the minimum size of theparentcontainer using this grid bag layout.Most applications do not call this method directly.
- Specified by:
minimumLayoutSizein interfaceLayoutManager- Parameters:
parent- the container in which to do the layout- Returns:
- the minimum size of the
parentcontainer - See Also:
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maximumLayoutSize
Returns the maximum dimensions for this layout given the components in the specified target container.- Specified by:
maximumLayoutSizein interfaceLayoutManager2- Parameters:
target- the container which needs to be laid out- Returns:
- the maximum dimensions for this layout
- See Also:
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getLayoutAlignmentX
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:
getLayoutAlignmentXin interfaceLayoutManager2- Parameters:
parent- the target container- Returns:
- the value
0.5fto indicate centered
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getLayoutAlignmentY
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:
getLayoutAlignmentYin interfaceLayoutManager2- Parameters:
parent- the target container- Returns:
- the value
0.5fto indicate centered
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invalidateLayout
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.- Specified by:
invalidateLayoutin interfaceLayoutManager2- Parameters:
target- the target container
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layoutContainer
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 thisGridBagLayoutobject.Most applications do not call this method directly.
- Specified by:
layoutContainerin interfaceLayoutManager- Parameters:
parent- the container in which to do the layout- See Also:
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toString
Returns a string representation of this grid bag layout's values. -
getLayoutInfo
Fills in an instance ofGridBagLayoutInfofor the current set of managed children. This requires three passes through the set of children:- Figure out the dimensions of the layout grid.
- Determine which cells the components occupy.
- Distribute the weights and min sizes among the rows/columns.
This method should only be used internally by
GridBagLayout.- Parameters:
parent- the layout containersizeflag- eitherPREFERREDSIZEorMINSIZE- Returns:
- the
GridBagLayoutInfofor the set of children - Since:
- 1.4
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GetLayoutInfo
This method is obsolete and supplied for backwards compatibility only; new code should callgetLayoutInfoinstead. Fills in an instance ofGridBagLayoutInfofor the current set of managed children. This method is the same asgetLayoutInfo; refer togetLayoutInfodescription for details.- Parameters:
parent- the layout containersizeflag- eitherPREFERREDSIZEorMINSIZE- Returns:
- the
GridBagLayoutInfofor the set of children
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adjustForGravity
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 byGridBagLayout.- Parameters:
constraints- the constraints to be appliedr- theRectangleto be adjusted- Since:
- 1.4
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AdjustForGravity
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
adjustForGravityinstead. This method is the same asadjustForGravity- Parameters:
constraints- the constraints to be appliedr- theRectangleto be adjusted
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getMinSize
Figures out the minimum size of the parent based on the information fromgetLayoutInfo. This method should only be used internally byGridBagLayout.- Parameters:
parent- the layout containerinfo- the layout info for this parent- Returns:
- a
Dimensionobject containing the minimum size - Since:
- 1.4
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GetMinSize
This method is obsolete and supplied for backwards compatibility only; new code should callgetMinSizeinstead. This method is the same asgetMinSize- Parameters:
parent- the layout containerinfo- the layout info for this parent- Returns:
- a
Dimensionobject containing the minimum size
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arrangeGrid
Lays out the grid. This method should only be used internally byGridBagLayout.- Parameters:
parent- the layout container- Since:
- 1.4
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ArrangeGrid
This method is obsolete and supplied for backwards compatibility only; new code should callarrangeGridinstead. This method is the same asarrangeGrid- Parameters:
parent- the layout container
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