Class GroupLayout

public class GroupLayout
extends Object
implements LayoutManager2

GroupLayout is a LayoutManager that hierarchically groups components in order to position them in a Container. GroupLayout is intended for use by builders, but may be hand-coded as well. Grouping is done by instances of the Group class. GroupLayout supports two types of groups. A sequential group positions its child elements sequentially, one after another. A parallel group aligns its child elements in one of four ways.

Each group may contain any number of elements, where an element is a Group, Component, or gap. A gap can be thought of as an invisible component with a minimum, preferred and maximum size. In addition GroupLayout supports a preferred gap, whose value comes from LayoutStyle.

Elements are similar to a spring. Each element has a range as specified by a minimum, preferred and maximum. Gaps have either a developer-specified range, or a range determined by LayoutStyle. The range for Components is determined from the Component's getMinimumSize, getPreferredSize and getMaximumSize methods. In addition, when adding Components you may specify a particular range to use instead of that from the component. The range for a Group is determined by the type of group. A ParallelGroup's range is the maximum of the ranges of its elements. A SequentialGroup's range is the sum of the ranges of its elements.

GroupLayout treats each axis independently. That is, there is a group representing the horizontal axis, and a group representing the vertical axis. The horizontal group is responsible for determining the minimum, preferred and maximum size along the horizontal axis as well as setting the x and width of the components contained in it. The vertical group is responsible for determining the minimum, preferred and maximum size along the vertical axis as well as setting the y and height of the components contained in it. Each Component must exist in both a horizontal and vertical group, otherwise an IllegalStateException is thrown during layout, or when the minimum, preferred or maximum size is requested.

The following diagram shows a sequential group along the horizontal axis. The sequential group contains three components. A parallel group was used along the vertical axis.

To reinforce that each axis is treated independently the diagram shows the range of each group and element along each axis. The range of each component has been projected onto the axes, and the groups are rendered in blue (horizontal) and red (vertical). For readability there is a gap between each of the elements in the sequential group.

The sequential group along the horizontal axis is rendered as a solid blue line. Notice the sequential group is the sum of the children elements it contains.

Along the vertical axis the parallel group is the maximum of the height of each of the components. As all three components have the same height, the parallel group has the same height.

The following diagram shows the same three components, but with the parallel group along the horizontal axis and the sequential group along the vertical axis.

As c1 is the largest of the three components, the parallel group is sized to c1. As c2 and c3 are smaller than c1 they are aligned based on the alignment specified for the component (if specified) or the default alignment of the parallel group. In the diagram c2 and c3 were created with an alignment of LEADING. If the component orientation were right-to-left then c2 and c3 would be positioned on the opposite side.

The following diagram shows a sequential group along both the horizontal and vertical axis.

GroupLayout provides the ability to insert gaps between Components. The size of the gap is determined by an instance of LayoutStyle. This may be turned on using the setAutoCreateGaps method. Similarly, you may use the setAutoCreateContainerGaps method to insert gaps between components that touch the edge of the parent container and the container.

The following builds a panel consisting of two labels in one column, followed by two textfields in the next column:

JComponent panel = ...;
   GroupLayout layout = new GroupLayout(panel);
   panel.setLayout(layout);

   // Turn on automatically adding gaps between components
   layout.setAutoCreateGaps(true);

   // Turn on automatically creating gaps between components that touch
   // the edge of the container and the container.
   layout.setAutoCreateContainerGaps(true);

   // Create a sequential group for the horizontal axis.

   GroupLayout.SequentialGroup hGroup = layout.createSequentialGroup();

   // The sequential group in turn contains two parallel groups.
   // One parallel group contains the labels, the other the text fields.
   // Putting the labels in a parallel group along the horizontal axis
   // positions them at the same x location.
   //
   // Variable indentation is used to reinforce the level of grouping.
   hGroup.addGroup(layout.createParallelGroup().
            addComponent(label1).addComponent(label2));
   hGroup.addGroup(layout.createParallelGroup().
            addComponent(tf1).addComponent(tf2));
   layout.setHorizontalGroup(hGroup);

   // Create a sequential group for the vertical axis.
   GroupLayout.SequentialGroup vGroup = layout.createSequentialGroup();

   // The sequential group contains two parallel groups that align
   // the contents along the baseline. The first parallel group contains
   // the first label and text field, and the second parallel group contains
   // the second label and text field. By using a sequential group
   // the labels and text fields are positioned vertically after one another.
   vGroup.addGroup(layout.createParallelGroup(Alignment.BASELINE).
            addComponent(label1).addComponent(tf1));
   vGroup.addGroup(layout.createParallelGroup(Alignment.BASELINE).
            addComponent(label2).addComponent(tf2));
   layout.setVerticalGroup(vGroup);

When run the following is produced.

This layout consists of the following.

• The horizontal axis consists of a sequential group containing two parallel groups. The first parallel group contains the labels, and the second parallel group contains the text fields.
• The vertical axis consists of a sequential group containing two parallel groups. The parallel groups are configured to align their components along the baseline. The first parallel group contains the first label and first text field, and the second group consists of the second label and second text field.

There are a couple of things to notice in this code:

• You need not explicitly add the components to the container; this is indirectly done by using one of the add methods of Group.
• The various add methods return the caller. This allows for easy chaining of invocations. For example, group.addComponent(label1).addComponent(label2); is equivalent to group.addComponent(label1); group.addComponent(label2);.
• There are no public constructors for Groups; instead use the create methods of GroupLayout.

Fields

DEFAULT_SIZE

public static final int DEFAULT_SIZE

Indicates the size from the component or gap should be used for a particular range value.

See Also:

GroupLayout.Group, Constant Field Values

PREFERRED_SIZE

public static final int PREFERRED_SIZE

Indicates the preferred size from the component or gap should be used for a particular range value.

See Also:

GroupLayout.Group, Constant Field Values

Constructors

GroupLayout

public GroupLayout(Container host)

Creates a GroupLayout for the specified Container.

Parameters:

host - the Container the GroupLayout is the LayoutManager for

Throws:

IllegalArgumentException - if host is null

Methods

setHonorsVisibility

public void setHonorsVisibility(boolean honorsVisibility)

Parameters:

honorsVisibility - whether component visibility is considered when sizing and positioning components

See Also:

setHonorsVisibility(Component,Boolean)

getHonorsVisibility

public boolean getHonorsVisibility()

Returns whether component visibility is considered when sizing and positioning components.

Returns:

whether component visibility is considered when sizing and positioning components

setHonorsVisibility

public void setHonorsVisibility(Component component,
                                Boolean honorsVisibility)

Parameters:

component - the component

honorsVisibility - whether visibility of this component should be considered for sizing and positioning

Throws:

IllegalArgumentException - if component is null

See Also:

setHonorsVisibility(Component,Boolean)

setAutoCreateGaps

public void setAutoCreateGaps(boolean autoCreatePadding)

Sets whether a gap between components should automatically be created. For example, if this is true and you add two components to a SequentialGroup a gap between the two components is automatically be created. The default is false.

Parameters:

autoCreatePadding - whether a gap between components is automatically created

getAutoCreateGaps

public boolean getAutoCreateGaps()

Returns true if gaps between components are automatically created.

Returns:

true if gaps between components are automatically created

setAutoCreateContainerGaps

public void setAutoCreateContainerGaps(boolean autoCreateContainerPadding)

Sets whether a gap between the container and components that touch the border of the container should automatically be created. The default is false.

Parameters:

autoCreateContainerPadding - whether a gap between the container and components that touch the border of the container should automatically be created

getAutoCreateContainerGaps

public boolean getAutoCreateContainerGaps()

Returns true if gaps between the container and components that border the container are automatically created.

Returns:

true if gaps between the container and components that border the container are automatically created

setHorizontalGroup

public void setHorizontalGroup(GroupLayout.Group group)

Sets the Group that positions and sizes components along the horizontal axis.

Parameters:

group - the Group that positions and sizes components along the horizontal axis

Throws:

IllegalArgumentException - if group is null

setVerticalGroup

public void setVerticalGroup(GroupLayout.Group group)

Sets the Group that positions and sizes components along the vertical axis.

Parameters:

group - the Group that positions and sizes components along the vertical axis

Throws:

IllegalArgumentException - if group is null

createSequentialGroup

public GroupLayout.SequentialGroup createSequentialGroup()

Creates and returns a SequentialGroup.

Returns:

a new SequentialGroup

createParallelGroup

public GroupLayout.ParallelGroup createParallelGroup()

Creates and returns a ParallelGroup with an alignment of Alignment.LEADING. This is a cover method for the more general createParallelGroup(Alignment) method.

Returns:

a new ParallelGroup

See Also:

createParallelGroup(Alignment)

createParallelGroup

public GroupLayout.ParallelGroup createParallelGroup(GroupLayout.Alignment alignment)

Creates and returns a ParallelGroup with the specified alignment. This is a cover method for the more general createParallelGroup(Alignment,boolean) method with true supplied for the second argument.

Parameters:

alignment - the alignment for the elements of the group

Returns:

a new ParallelGroup

Throws:

IllegalArgumentException - if alignment is null

See Also:

createBaselineGroup(boolean, boolean), GroupLayout.ParallelGroup

createParallelGroup

public GroupLayout.ParallelGroup createParallelGroup(GroupLayout.Alignment alignment,
                                                     boolean resizable)

Parameters:

alignment - the alignment for the elements of the group

resizable - true if the group is resizable; if the group is not resizable the preferred size is used for the minimum and maximum size of the group

Returns:

a new ParallelGroup

Throws:

IllegalArgumentException - if alignment is null

See Also:

createBaselineGroup(boolean, boolean), GroupLayout.ParallelGroup

createBaselineGroup

public GroupLayout.ParallelGroup createBaselineGroup(boolean resizable,
                                                     boolean anchorBaselineToTop)

Creates and returns a ParallelGroup that aligns it's elements along the baseline.

Parameters:

resizable - whether the group is resizable

anchorBaselineToTop - whether the baseline is anchored to the top or bottom of the group

See Also:

createBaselineGroup(boolean, boolean), GroupLayout.ParallelGroup

linkSize

public void linkSize(Component... components)

Parameters:

components - the Components that are to have the same size

Throws:

IllegalArgumentException - if components is null, or contains null

See Also:

linkSize(int,Component[])

linkSize

public void linkSize(int axis,
                     Component... components)

Parameters:

components - the Components that are to have the same size

axis - the axis to link the size along; one of SwingConstants.HORIZONTAL or SwingConstans.VERTICAL

Throws:

IllegalArgumentException - if components is null, or contains null; or axis is not SwingConstants.HORIZONTAL or SwingConstants.VERTICAL

replace

public void replace(Component existingComponent,
                    Component newComponent)

Replaces an existing component with a new one.

Parameters:

existingComponent - the component that should be removed and replaced with newComponent

newComponent - the component to put in existingComponent's place

Throws:

IllegalArgumentException - if either of the components are null or existingComponent is not being managed by this layout manager

setLayoutStyle

public void setLayoutStyle(LayoutStyle layoutStyle)

Sets the LayoutStyle used to calculate the preferred gaps between components. A value of null indicates the shared instance of LayoutStyle should be used.

Parameters:

layoutStyle - the LayoutStyle to use

See Also:

LayoutStyle

getLayoutStyle

public LayoutStyle getLayoutStyle()

Returns the LayoutStyle used for calculating the preferred gap between components. This returns the value specified to setLayoutStyle, which may be null.

Returns:

the LayoutStyle used for calculating the preferred gap between components

addLayoutComponent

public void addLayoutComponent(String name,
                               Component component)

Notification that a Component has been added to the parent container. You should not invoke this method directly, instead you should use one of the Group methods to add a Component.

Specified by:

addLayoutComponent in interface LayoutManager

Parameters:

name - the string to be associated with the component

component - the Component to be added

removeLayoutComponent

public void removeLayoutComponent(Component component)

Notification that a Component has been removed from the parent container. You should not invoke this method directly, instead invoke remove on the parent Container.

Specified by:

removeLayoutComponent in interface LayoutManager

Parameters:

component - the component to be removed

See Also:

Component.remove(java.awt.MenuComponent)

preferredLayoutSize

public Dimension preferredLayoutSize(Container parent)

Returns the preferred size for the specified container.

Specified by:

preferredLayoutSize in interface LayoutManager

Parameters:

parent - the container to return the preferred size for

Returns:

the preferred size for parent

Throws:

IllegalArgumentException - if parent is not the same Container this was created with

IllegalStateException - if any of the components added to this layout are not in both a horizontal and vertical group

See Also:

Container.getPreferredSize()

minimumLayoutSize

public Dimension minimumLayoutSize(Container parent)

Returns the minimum size for the specified container.

Specified by:

minimumLayoutSize in interface LayoutManager

Parameters:

parent - the container to return the size for

Returns:

the minimum size for parent

Throws:

IllegalArgumentException - if parent is not the same Container that this was created with

IllegalStateException - if any of the components added to this layout are not in both a horizontal and vertical group

See Also:

Container.getMinimumSize()

layoutContainer

public void layoutContainer(Container parent)

Lays out the specified container.

Specified by:

layoutContainer in interface LayoutManager

Parameters:

parent - the container to be laid out

Throws:

IllegalStateException - if any of the components added to this layout are not in both a horizontal and vertical group

addLayoutComponent

public void addLayoutComponent(Component component,
                               Object constraints)

Notification that a Component has been added to the parent container. You should not invoke this method directly, instead you should use one of the Group methods to add a Component.

Specified by:

addLayoutComponent in interface LayoutManager2

Parameters:

component - the component added

constraints - description of where to place the component

maximumLayoutSize

public Dimension maximumLayoutSize(Container parent)

Returns the maximum size for the specified container.

Specified by:

maximumLayoutSize in interface LayoutManager2

Parameters:

parent - the container to return the size for

Returns:

the maximum size for parent

Throws:

IllegalArgumentException - if parent is not the same Container that this was created with

IllegalStateException - if any of the components added to this layout are not in both a horizontal and vertical group

See Also:

Container.getMaximumSize()

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 Container hosting this LayoutManager

Returns:

the alignment; this implementation returns .5

Throws:

IllegalArgumentException - if parent is not the same Container that this was created with

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 Container hosting this LayoutManager

Returns:

alignment; this implementation returns .5

Throws:

IllegalArgumentException - if parent is not the same Container that this was created with

invalidateLayout

public void invalidateLayout(Container parent)

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

Specified by:

invalidateLayout in interface LayoutManager2

Parameters:

parent - the Container hosting this LayoutManager

Throws:

IllegalArgumentException - if parent is not the same Container that this was created with

toString

public String toString()

Returns a string representation of this GroupLayout. This method is intended to be used for debugging purposes, and the content and format of the returned string may vary between implementations.

Overrides:

toString in class Object

Returns:

a string representation of this GroupLayout