Module java.desktop
Package java.awt

# Class BorderLayout

java.lang.Object
java.awt.BorderLayout

All Implemented Interfaces:
  `LayoutManager`, `LayoutManager2`, `Serializable`

public class BorderLayout extends Object implements LayoutManager2, Serializable
A border layout lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center. Each region may contain no more than one component, and is identified by a corresponding constant: `NORTH`, `SOUTH`, `EAST`, `WEST`, and `CENTER`. When adding a component to a container with a border layout, use one of these five constants, for example:

        Panel p = new Panel();
        p.setLayout(new BorderLayout());
        p.add(new Button("Okay"), BorderLayout.SOUTH);

As a convenience, `BorderLayout` interprets the absence of a string specification the same as the constant `CENTER`:

        Panel p2 = new Panel();
        p2.setLayout(new BorderLayout());
        p2.add(new TextArea());  // Same as p.add(new TextArea(), BorderLayout.CENTER);

In addition, `BorderLayout` supports the relative positioning constants, `PAGE_START`, `PAGE_END`, `LINE_START`, and `LINE_END`. In a container whose `ComponentOrientation` is set to `ComponentOrientation.LEFT_TO_RIGHT`, these constants map to `NORTH`, `SOUTH`, `WEST`, and `EAST`, respectively.

For compatibility with previous releases, `BorderLayout` also includes the relative positioning constants `BEFORE_FIRST_LINE`, `AFTER_LAST_LINE`, `BEFORE_LINE_BEGINS` and `AFTER_LINE_ENDS`. These are equivalent to `PAGE_START`, `PAGE_END`, `LINE_START` and `LINE_END` respectively. For consistency with the relative positioning constants used by other components, the latter constants are preferred.

Mixing both absolute and relative positioning constants can lead to unpredictable results. If you use both types, the relative constants will take precedence. For example, if you add components using both the `NORTH` and `PAGE_START` constants in a container whose orientation is `LEFT_TO_RIGHT`, only the `PAGE_START` will be laid out.

NOTE: Currently, `BorderLayout` does not support vertical orientations. The `isVertical` setting on the container's `ComponentOrientation` is not respected.

The components are laid out according to their preferred sizes and the constraints of the container's size. The `NORTH` and `SOUTH` components may be stretched horizontally; the `EAST` and `WEST` components may be stretched vertically; the `CENTER` component may stretch both horizontally and vertically to fill any space left over.

Here is an example of five buttons in an applet laid out using the `BorderLayout` layout manager:

The code for this applet is as follows:

>      import java.awt.*;
>      import java.applet.Applet;

>      public class buttonDir extends Applet {
>        public void init() {
>          setLayout(new BorderLayout());
>          add(new Button("North"), BorderLayout.NORTH);
>          add(new Button("South"), BorderLayout.SOUTH);
>          add(new Button("East"), BorderLayout.EAST);
>          add(new Button("West"), BorderLayout.WEST);
>          add(new Button("Center"), BorderLayout.CENTER);
>        }
>      }

Since:
  1.0
See Also:
  - `Container.add(String, Component)`
  - `ComponentOrientation`
  - Serialized Form

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final String`
  `AFTER_LAST_LINE`
  Synonym for PAGE_END.
  `static final String`
  `AFTER_LINE_ENDS`
  Synonym for LINE_END.
  `static final String`
  `BEFORE_FIRST_LINE`
  Synonym for PAGE_START.
  `static final String`
  `BEFORE_LINE_BEGINS`
  Synonym for LINE_START.
  `static final String`
  `CENTER`
  The center layout constraint (middle of container).
  `static final String`
  `EAST`
  The east layout constraint (right side of container).
  `static final String`
  `LINE_END`
  The component goes at the end of the line direction for the layout.
  `static final String`
  `LINE_START`
  The component goes at the beginning of the line direction for the layout.
  `static final String`
  `NORTH`
  The north layout constraint (top of container).
  `static final String`
  `PAGE_END`
  The component comes after the last line of the layout's content.
  `static final String`
  `PAGE_START`
  The component comes before the first line of the layout's content.
  `static final String`
  `SOUTH`
  The south layout constraint (bottom of container).
  `static final String`
  `WEST`
  The west layout constraint (left side of container).

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `BorderLayout()`
  Constructs a new border layout with no gaps between components.
  `BorderLayout(int hgap, int vgap)`
  Constructs a border layout with the specified gaps between components.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addLayoutComponent(Component comp, Object constraints)`
  Adds the specified component to the layout, using the specified constraint object.
  `void`
  `addLayoutComponent(String name, Component comp)`
  Deprecated.
  replaced by `addLayoutComponent(Component, Object)`.
  `Object`
  `getConstraints(Component comp)`
  Gets the constraints for the specified component
  `int`
  `getHgap()`
  Returns the horizontal gap between components.
  `float`
  `getLayoutAlignmentX(Container parent)`
  Returns the alignment along the x axis.
  `float`
  `getLayoutAlignmentY(Container parent)`
  Returns the alignment along the y axis.
  `Component`
  `getLayoutComponent(Container target, Object constraints)`
  Returns the component that corresponds to the given constraint location based on the target `Container`'s component orientation.
  `Component`
  `getLayoutComponent(Object constraints)`
  Gets the component that was added using the given constraint
  `int`
  `getVgap()`
  Returns the vertical gap between components.
  `void`
  `invalidateLayout(Container target)`
  Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
  `void`
  `layoutContainer(Container target)`
  Lays out the container argument using this border layout.
  `Dimension`
  `maximumLayoutSize(Container target)`
  Returns the maximum dimensions for this layout given the components in the specified target container.
  `Dimension`
  `minimumLayoutSize(Container target)`
  Determines the minimum size of the `target` container using this layout manager.
  `Dimension`
  `preferredLayoutSize(Container target)`
  Determines the preferred size of the `target` container using this layout manager, based on the components in the container.
  `void`
  `removeLayoutComponent(Component comp)`
  Removes the specified component from this border layout.
  `void`
  `setHgap(int hgap)`
  Sets the horizontal gap between components.
  `void`
  `setVgap(int vgap)`
  Sets the vertical gap between components.
  `String`
  `toString()`
  Returns a string representation of the state of this border layout.

  ### Methods declared in class java.lang.Object

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

- ## Field Details

  - ### NORTH

    public static final String NORTH
    The north layout constraint (top of container).
    See Also:
      - Constant Field Values

  - ### SOUTH

    public static final String SOUTH
    The south layout constraint (bottom of container).
    See Also:
      - Constant Field Values

  - ### EAST

    public static final String EAST
    The east layout constraint (right side of container).
    See Also:
      - Constant Field Values

  - ### WEST

    public static final String WEST
    The west layout constraint (left side of container).
    See Also:
      - Constant Field Values

  - ### CENTER

    public static final String CENTER
    The center layout constraint (middle of container).
    See Also:
      - Constant Field Values

  - ### BEFORE_FIRST_LINE

    public static final String BEFORE_FIRST_LINE
    Synonym for PAGE_START. Exists for compatibility with previous versions. PAGE_START is preferred.
    Since:
      1.2
    See Also:
      - `PAGE_START`
      - Constant Field Values

  - ### AFTER_LAST_LINE

    public static final String AFTER_LAST_LINE
    Synonym for PAGE_END. Exists for compatibility with previous versions. PAGE_END is preferred.
    Since:
      1.2
    See Also:
      - `PAGE_END`
      - Constant Field Values

  - ### BEFORE_LINE_BEGINS

    public static final String BEFORE_LINE_BEGINS
    Synonym for LINE_START. Exists for compatibility with previous versions. LINE_START is preferred.
    Since:
      1.2
    See Also:
      - `LINE_START`
      - Constant Field Values

  - ### AFTER_LINE_ENDS

    public static final String AFTER_LINE_ENDS
    Synonym for LINE_END. Exists for compatibility with previous versions. LINE_END is preferred.
    Since:
      1.2
    See Also:
      - `LINE_END`
      - Constant Field Values

  - ### PAGE_START

    public static final String PAGE_START
    The component comes before the first line of the layout's content. For Western, left-to-right and top-to-bottom orientations, this is equivalent to NORTH.
    Since:
      1.4
    See Also:
      - `Component.getComponentOrientation()`
      - Constant Field Values

  - ### PAGE_END

    public static final String PAGE_END
    The component comes after the last line of the layout's content. For Western, left-to-right and top-to-bottom orientations, this is equivalent to SOUTH.
    Since:
      1.4
    See Also:
      - `Component.getComponentOrientation()`
      - Constant Field Values

  - ### LINE_START

    public static final String LINE_START
    The component goes at the beginning of the line direction for the layout. For Western, left-to-right and top-to-bottom orientations, this is equivalent to WEST.
    Since:
      1.4
    See Also:
      - `Component.getComponentOrientation()`
      - Constant Field Values

  - ### LINE_END

    public static final String LINE_END
    The component goes at the end of the line direction for the layout. For Western, left-to-right and top-to-bottom orientations, this is equivalent to EAST.
    Since:
      1.4
    See Also:
      - `Component.getComponentOrientation()`
      - Constant Field Values

- ## Constructor Details

  - ### BorderLayout

    public BorderLayout()
    Constructs a new border layout with no gaps between components.

  - ### BorderLayout

    public BorderLayout(int hgap, int vgap)
    Constructs a border layout with the specified gaps between components. The horizontal gap is specified by `hgap` and the vertical gap is specified by `vgap`.
    Parameters:
      `hgap` - the horizontal gap.
      `vgap` - the vertical gap.

- ## Method Details

  - ### getHgap

    public int getHgap()
    Returns the horizontal gap between components.
    Returns:
      the horizontal gap between components
    Since:
      1.1

  - ### setHgap

    public void setHgap(int hgap)
    Sets the horizontal gap between components.
    Parameters:
      `hgap` - the horizontal gap between components
    Since:
      1.1

  - ### getVgap

    public int getVgap()
    Returns the vertical gap between components.
    Returns:
      the vertical gap between components
    Since:
      1.1

  - ### setVgap

    public void setVgap(int vgap)
    Sets the vertical gap between components.
    Parameters:
      `vgap` - the vertical gap between components
    Since:
      1.1

  - ### addLayoutComponent

    public void addLayoutComponent(Component comp, Object constraints)
    Adds the specified component to the layout, using the specified constraint object. For border layouts, the constraint must be one of the following constants: `NORTH`, `SOUTH`, `EAST`, `WEST`, or `CENTER`.

    Most applications do not call this method directly. This method is called when a component is added to a container using the `Container.add` method with the same argument types.

    Specified by:
      `addLayoutComponent` in interface `LayoutManager2`
    Parameters:
      `comp` - the component to be added.
      `constraints` - an object that specifies how and where the component is added to the layout.
    Throws:
      `IllegalArgumentException` - if the constraint object is not a string, or if it not one of the five specified constants.
    Since:
      1.1
    See Also:
      - `Container.add(java.awt.Component, java.lang.Object)`

  - ### addLayoutComponent

    @Deprecated public void addLayoutComponent(String name, Component comp)
    Deprecated.
    replaced by `addLayoutComponent(Component, Object)`.
    Description copied from interface: `LayoutManager`
    If the layout manager uses a per-component string, adds the component `comp` to the layout, associating it with the string specified by `name`.
    Specified by:
      `addLayoutComponent` in interface `LayoutManager`
    Parameters:
      `name` - the string to be associated with the component
      `comp` - the component to be added

  - ### removeLayoutComponent

    public void removeLayoutComponent(Component comp)
    Removes the specified component from this border layout. This method is called when a container calls its `remove` or `removeAll` methods. Most applications do not call this method directly.
    Specified by:
      `removeLayoutComponent` in interface `LayoutManager`
    Parameters:
      `comp` - the component to be removed.
    See Also:
      - `Container.remove(java.awt.Component)`
      - `Container.removeAll()`

  - ### getLayoutComponent

    public Component getLayoutComponent(Object constraints)
    Gets the component that was added using the given constraint
    Parameters:
      `constraints` - the desired constraint, one of `CENTER`, `NORTH`, `SOUTH`, `WEST`, `EAST`, `PAGE_START`, `PAGE_END`, `LINE_START`, `LINE_END`
    Returns:
      the component at the given location, or `null` if the location is empty
    Throws:
      `IllegalArgumentException` - if the constraint object is not one of the nine specified constants
    Since:
      1.5
    See Also:
      - `addLayoutComponent(java.awt.Component, java.lang.Object)`

  - ### getLayoutComponent

    public Component getLayoutComponent(Container target, Object constraints)
    Returns the component that corresponds to the given constraint location based on the target `Container`'s component orientation. Components added with the relative constraints `PAGE_START`, `PAGE_END`, `LINE_START`, and `LINE_END` take precedence over components added with the explicit constraints `NORTH`, `SOUTH`, `WEST`, and `EAST`. The `Container`'s component orientation is used to determine the location of components added with `LINE_START` and `LINE_END`.
    Parameters:
      `target` - the `Container` used to obtain the constraint location based on the target `Container`'s component orientation.
      `constraints` - the desired absolute position, one of `CENTER`, `NORTH`, `SOUTH`, `EAST`, `WEST`
    Returns:
      the component at the given location, or `null` if the location is empty
    Throws:
      `IllegalArgumentException` - if the constraint object is not one of the five specified constants
      `NullPointerException` - if the target parameter is null
    Since:
      1.5
    See Also:
      - `addLayoutComponent(java.awt.Component, java.lang.Object)`

  - ### getConstraints

    public Object getConstraints(Component comp)
    Gets the constraints for the specified component
    Parameters:
      `comp` - the component to be queried
    Returns:
      the constraint for the specified component, or null if component is null or is not present in this layout
    Since:
      1.5
    See Also:
      - `addLayoutComponent(java.awt.Component, java.lang.Object)`

  - ### minimumLayoutSize

    public Dimension minimumLayoutSize(Container target)
    Determines the minimum size of the `target` container using this layout manager.

    This method is called when a container calls its `getMinimumSize` method. Most applications do not call this method directly.

    Specified by:
      `minimumLayoutSize` in interface `LayoutManager`
    Parameters:
      `target` - the container in which to do the layout.
    Returns:
      the minimum dimensions needed to lay out the subcomponents of the specified container.
    See Also:
      - `Container`
      - `preferredLayoutSize(java.awt.Container)`
      - `Container.getMinimumSize()`

  - ### preferredLayoutSize

    public Dimension preferredLayoutSize(Container target)
    Determines the preferred size of the `target` container using this layout manager, based on the components in the container.

    Most applications do not call this method directly. This method is called when a container calls its `getPreferredSize` method.

    Specified by:
      `preferredLayoutSize` in interface `LayoutManager`
    Parameters:
      `target` - the container in which to do the layout.
    Returns:
      the preferred dimensions to lay out the subcomponents of the specified container.
    See Also:
      - `Container`
      - `minimumLayoutSize(java.awt.Container)`
      - `Container.getPreferredSize()`

  - ### 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 component which needs to be laid out
    Returns:
      the maximum size of the container
    See Also:
      - `Container`
      - `minimumLayoutSize(java.awt.Container)`
      - `preferredLayoutSize(java.awt.Container)`

  - ### getLayoutAlignmentX

    public float getLayoutAlignmentX(Container parent)
    Returns the alignment along the x axis. This specifies how the component would like to be aligned relative to other components. The value should be a number between 0 and 1 where 0 represents alignment along the origin, 1 is aligned the furthest away from the origin, 0.5 is centered, etc.
    Specified by:
      `getLayoutAlignmentX` in interface `LayoutManager2`
    Parameters:
      `parent` - the target container
    Returns:
      the x-axis alignment preference

  - ### 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 y-axis alignment preference

  - ### 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 target)
    Lays out the container argument using this border layout.

    This method actually reshapes the components in the specified container in order to satisfy the constraints of this `BorderLayout` object. The `NORTH` and `SOUTH` components, if any, are placed at the top and bottom of the container, respectively. The `WEST` and `EAST` components are then placed on the left and right, respectively. Finally, the `CENTER` object is placed in any remaining space in the middle.

    Most applications do not call this method directly. This method is called when a container calls its `doLayout` method.

    Specified by:
      `layoutContainer` in interface `LayoutManager`
    Parameters:
      `target` - the container in which to do the layout.
    See Also:
      - `Container`
      - `Container.doLayout()`

  - ### toString

    public String toString()
    Returns a string representation of the state of this border layout.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of this border layout.