# Class GroupLayout

java.lang.Object
javax.swing.GroupLayout

All Implemented Interfaces:
  `LayoutManager, LayoutManager2`

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 `Component`s is determined from the `Component`'s `getMinimumSize`, `getPreferredSize` and `getMaximumSize` methods. In addition, when adding `Component`s 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 `Component`s. 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 `Group`s; instead use the create methods of `GroupLayout`.

Since:
  1.6

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static enum`
  `GroupLayout.Alignment`
  Enumeration of the possible ways `ParallelGroup` can align its children.
  `class`
  `GroupLayout.Group`
  `Group` provides the basis for the two types of operations supported by `GroupLayout`: laying out components one after another (`SequentialGroup`) or aligned (`ParallelGroup`).
  `class`
  `GroupLayout.ParallelGroup`
  A `Group` that aligns and sizes its children.
  `final class`
  `GroupLayout.SequentialGroup`
  A `Group` that positions and sizes its elements sequentially, one after another.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final int`
  `DEFAULT_SIZE`
  Indicates the size from the component or gap should be used for a particular range value.
  `static final int`
  `PREFERRED_SIZE`
  Indicates the preferred size from the component or gap should be used for a particular range value.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `GroupLayout(Container host)`
  Creates a `GroupLayout` for the specified `Container`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addLayoutComponent(Component component, Object constraints)`
  Notification that a `Component` has been added to the parent container.
  `void`
  `addLayoutComponent(String name, Component component)`
  Notification that a `Component` has been added to the parent container.
  `GroupLayout.ParallelGroup`
  `createBaselineGroup(boolean resizable, boolean anchorBaselineToTop)`
  Creates and returns a `ParallelGroup` that aligns its elements along the baseline.
  `GroupLayout.ParallelGroup`
  `createParallelGroup()`
  Creates and returns a `ParallelGroup` with an alignment of `Alignment.LEADING`.
  `GroupLayout.ParallelGroup`
  `createParallelGroup(GroupLayout.Alignment alignment)`
  Creates and returns a `ParallelGroup` with the specified alignment.
  `GroupLayout.ParallelGroup`
  `createParallelGroup(GroupLayout.Alignment alignment, boolean resizable)`
  Creates and returns a `ParallelGroup` with the specified alignment and resize behavior.
  `GroupLayout.SequentialGroup`
  `createSequentialGroup()`
  Creates and returns a `SequentialGroup`.
  `boolean`
  `getAutoCreateContainerGaps()`
  Returns `true` if gaps between the container and components that border the container are automatically created.
  `boolean`
  `getAutoCreateGaps()`
  Returns `true` if gaps between components are automatically created.
  `boolean`
  `getHonorsVisibility()`
  Returns whether component visibility is considered when sizing and positioning components.
  `float`
  `getLayoutAlignmentX(Container parent)`
  Returns the alignment along the x axis.
  `float`
  `getLayoutAlignmentY(Container parent)`
  Returns the alignment along the y axis.
  `LayoutStyle`
  `getLayoutStyle()`
  Returns the `LayoutStyle` used for calculating the preferred gap between components.
  `void`
  `invalidateLayout(Container parent)`
  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.
  `void`
  `linkSize(int axis, Component... components)`
  Forces the specified components to have the same size along the specified axis regardless of their preferred, minimum or maximum sizes.
  `void`
  `linkSize(Component... components)`
  Forces the specified components to have the same size regardless of their preferred, minimum or maximum sizes.
  `Dimension`
  `maximumLayoutSize(Container parent)`
  Returns the maximum size for the specified container.
  `Dimension`
  `minimumLayoutSize(Container parent)`
  Returns the minimum size for the specified container.
  `Dimension`
  `preferredLayoutSize(Container parent)`
  Returns the preferred size for the specified container.
  `void`
  `removeLayoutComponent(Component component)`
  Notification that a `Component` has been removed from the parent container.
  `void`
  `replace(Component existingComponent, Component newComponent)`
  Replaces an existing component with a new one.
  `void`
  `setAutoCreateContainerGaps(boolean autoCreateContainerPadding)`
  Sets whether a gap between the container and components that touch the border of the container should automatically be created.
  `void`
  `setAutoCreateGaps(boolean autoCreatePadding)`
  Sets whether a gap between components should automatically be created.
  `void`
  `setHonorsVisibility(boolean honorsVisibility)`
  Sets whether component visibility is considered when sizing and positioning components.
  `void`
  `setHonorsVisibility(Component component, Boolean honorsVisibility)`
  Sets whether the component's visibility is considered for sizing and positioning.
  `void`
  `setHorizontalGroup(GroupLayout.Group group)`
  Sets the `Group` that positions and sizes components along the horizontal axis.
  `void`
  `setLayoutStyle(LayoutStyle layoutStyle)`
  Sets the `LayoutStyle` used to calculate the preferred gaps between components.
  `void`
  `setVerticalGroup(GroupLayout.Group group)`
  Sets the `Group` that positions and sizes components along the vertical axis.
  `String`
  `toString()`
  Returns a string representation of this `GroupLayout`.

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- ## Field Details

  - ### 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

- ## Constructor Details

  - ### 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`

- ## Method Details

  - ### setHonorsVisibility

    public void setHonorsVisibility(boolean honorsVisibility)
    Sets whether component visibility is considered when sizing and positioning components. A value of `true` indicates that non-visible components should not be treated as part of the layout. A value of `false` indicates that components should be positioned and sized regardless of visibility.

    A value of `false` is useful when the visibility of components is dynamically adjusted and you don't want surrounding components and the sizing to change.

    The specified value is used for components that do not have an explicit visibility specified.

    The default is `true`.

    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)
    Sets whether the component's visibility is considered for sizing and positioning. A value of `Boolean.TRUE` indicates that if `component` is not visible it should not be treated as part of the layout. A value of `false` indicates that `component` is positioned and sized regardless of its visibility. A value of `null` indicates the value specified by the single argument method `setHonorsVisibility` should be used.

    If `component` is not a child of the `Container` this `GroupLayout` is managing, it will be added to the `Container`.

    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)
    Creates and returns a `ParallelGroup` with the specified alignment and resize behavior. The `alignment` argument specifies how children elements are positioned that do not fill the group. For example, if a `ParallelGroup` with an alignment of `TRAILING` is given 100 and a child only needs 50, the child is positioned at the position 50 (with a component orientation of left-to-right).

    Baseline alignment is only useful when used along the vertical axis. A `ParallelGroup` created with a baseline alignment along the horizontal axis is treated as `LEADING`.

    Refer to `ParallelGroup` for details on the behavior of baseline groups.

    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 its 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
    Returns:
      the `ParallelGroup`
    See Also:
      - `createBaselineGroup(boolean, boolean)`
      - `GroupLayout.ParallelGroup`

  - ### linkSize

    public void linkSize(Component... components)
    Forces the specified components to have the same size regardless of their preferred, minimum or maximum sizes. Components that are linked are given the maximum of the preferred size of each of the linked components. For example, if you link two components with a preferred width of 10 and 20, both components are given a width of 20.

    This can be used multiple times to force any number of components to share the same size.

    Linked Components are not be resizable.

    Parameters:
      `components` - the `Component`s 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)
    Forces the specified components to have the same size along the specified axis regardless of their preferred, minimum or maximum sizes. Components that are linked are given the maximum of the preferred size of each of the linked components. For example, if you link two components along the horizontal axis and the preferred width is 10 and 20, both components are given a width of 20.

    This can be used multiple times to force any number of components to share the same size.

    Linked `Component`s are not be resizable.

    Parameters:
      `axis` - the axis to link the size along; one of `SwingConstants.HORIZONTAL` or `SwingConstants.VERTICAL`
      `components` - the `Component`s that are to have the same size
    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(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`