IT. Expert System.

Java Standard Edition (SE)

BorderLayout


java.awt

Class 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 layed out.

    NOTE: Currently (in the Java 2 platform v1.2), 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:

    diagram of an applet demonstrating borderlayout.
      each section of the borderlayout contains a button corresponding to its position in the layout, one of:
      north, west, center, east, or south.

    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:
    JDK1.0
    See Also:
    Container.add(String, Component), ComponentOrientation, Serialized Form
    • Constructor Detail

      • 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 Detail

      • getHgap

        public int getHgap()
        Returns the horizontal gap between components.
        Since:
        JDK1.1
      • setHgap

        public void setHgap(int hgap)
        Sets the horizontal gap between components.
        Parameters:
        hgap - the horizontal gap between components
        Since:
        JDK1.1
      • getVgap

        public int getVgap()
        Returns the vertical gap between components.
        Since:
        JDK1.1
      • setVgap

        public void setVgap(int vgap)
        Sets the vertical gap between components.
        Parameters:
        vgap - the vertical gap between components
        Since:
        JDK1.1
      • 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:
        JDK1.1
        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
      • 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:
        constraints - the desired absolute position, one of CENTER, NORTH, SOUTH, EAST, WEST
        target - the Container used to obtain the constraint location based on the target Container's component orientation.
        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)
      • 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()
      • 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
      • 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
      • 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
      • 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.


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