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Java AWT

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Layouts
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7.11 The sun.awt Layout Collection

The sun.awt package defines four additional layouts. The first two, HorizBagLayout and VerticalBagLayout, are available only when used with Sun's JDK or Internet Explorer, since they are not provided with Netscape Navigator and may not be available from other vendors. Therefore, these layout managers should be used selectively within applets. The third layout manager, VariableGridLayout, is available with Netscape Navigator 2.0 or 3.0 and Internet Explorer. Usage of this layout manager is safer within applets but is still at your own risk. The final layout manager is introduced in Java 1.1, OrientableFlowLayout. Only time will tell where that one will be available. Any of these layout managers could be moved into a future version of java.awt if there is enough interest.

HorizBagLayout

In a HorizBagLayout, the components are all arranged in a single row, from left to right. The height of each component is the height of the container; the width of each component is its preferred width. Figure 7.16 shows HorizBagLayout in use.

Constructors

public HorizBagLayout ()

This constructor creates a HorizBagLayout with a horizontal gap of zero pixels. The gap is the space between the different components in the horizontal direction.

public HorizBagLayout (int hgap)

This constructor creates a HorizBagLayout using a horizontal gap of hgap pixels.

LayoutManager methods

public void addLayoutComponent (String name, Component component)

The addLayoutComponent() method of HorizBagLayout does nothing.

public void removeLayoutComponent (Component component)

The removeLayoutComponent() method of HorizBagLayout does nothing.

public Dimension preferredLayoutSize (Container target)

The preferredLayoutSize() method of HorizBagLayout sums up the preferred widths of all the components in target, along with the hgap and right and left insets to get the width of the target. The height returned will be the preferred height of the tallest component.

public Dimension minimumLayoutSize (Container target)

The minimumLayoutSize() method of HorizBagLayout sums up the minimum widths of all the components in target, along with the hgap and right and left insets to get the width of the target. The height returned will be the minimum height of the tallest component.

public void layoutContainer (Container target)

The layoutContainer() method draws target's components on the screen in one row. The height of each component is the height of the container. Each component's width is its preferred width, if enough space is available.

Miscellaneous methods

public String toString ()

The toString() method of HorizBagLayout returns a string with the current horizontal gap setting--for example:

sun.awt.HorizBagLayout[hgap=0]

VerticalBagLayout

The VerticalBagLayout places all the components in a single column. The width of each component is the width of the container; each component is given its preferred height. Figure 7.17 shows VerticalBagLayout in use.

Constructors

public VerticalBagLayout ()

This constructor creates a VerticalBagLayout with a vertical gap of zero pixels. The gap is the space between components in the vertical direction. With a gap of 0, adjacent components will touch each other.

public VerticalBagLayout (int vgap)

This constructor creates a VerticalBagLayout with a vertical gap of vgap pixels.

LayoutManager methods

public void addLayoutComponent (String name, Component component)

The addLayoutComponent() method of VerticalBagLayout does nothing.

public void removeLayoutComponent (Component component)

The removeLayoutComponent() method of VerticalBagLayout does nothing.

public Dimension preferredLayoutSize (Container target)

To get the preferred height of the layout, the preferredLayoutSize() method sums up the preferred height of all the components in target along with the vgap and top and bottom insets. For the preferred width, preferredLayoutSize() returns the preferred width of the widest component.

public Dimension minimumLayoutSize (Container target)

To get the minimum height of the layout, the minimumLayoutSize() method sums up the minimum height of all the components in target along with the vgap and top and bottom insets. For the minimum width, minimumLayoutSize() returns the minimum width of the widest component.

public void layoutContainer (Container target)

The layoutContainer() method draws target's components on the screen in one column. The width of each component is the width of the container. Each component's height is its preferredSize() height, if available.

Miscellaneous methods

public String toString ()

The toString() method of VerticalBagLayout returns a string with the current vertical gap setting. For example:

sun.awt.VerticalBagLayout[vgap=0]

VariableGridLayout

The VariableGridLayout builds upon the GridLayout. It arranges components on a grid of rows and columns. However, instead of giving all components the same size, the VariableGridLayout allows you to size rows and columns fractionally. Another difference between VariableGridLayout and GridBagLayout is that a VariableGridLayout has a fixed size. If you ask for a 3x3 grid, you will get exactly that. The layout manager throws the ArrayIndexOutOfBoundsException run-time exception if you try to add too many components.

Figure 7.18 shows a VariableGridLayout in which row one takes up 50 percent of the screen, and rows two and three take up 25 percent of the screen each. Column one takes up 50 percent of the screen; columns two and three take 25 percent each.

Here is the code that creates Figure 7.18:

import java.awt.*;
java.applet.Applet;
import sun.awt.VariableGridLayout;
public class vargrid extends Applet {
    public void init () {
        VariableGridLayout vgl;
        setLayout (vgl = new VariableGridLayout (3,3));
        vgl.setRowFraction (0, 1.0/2.0);
        vgl.setRowFraction (1, 1.0/4.0);
        vgl.setRowFraction (2, 1.0/4.0);
        vgl.setColFraction (0, 1.0/2.0);
        vgl.setColFraction (1, 1.0/4.0);
        vgl.setColFraction (2, 1.0/4.0);
        add (new Button ("One"));
        add (new Button ("Two"));
        add (new Button ("Three"));
        add (new Button ("Four"));
        add (new Button ("Five"));
        add (new Button ("Six"));
        add (new Button ("Seven"));
        add (new Button ("Eight"));
        add (new Button ("Nine"));
    }
}
Constructors

public VariableGridLayout (int rows, int columns)

This constructor creates a VariableGridLayout with the specified number of rows and columns. You cannot specify zero for one dimension. If either rows or columns is zero, the constructor throws the NullPointerException run-time exception. This constructor uses the default values for horizontal and vertical gaps (zero pixels), which means that components in adjacent cells will touch each other.

public VariableGridLayout (int rows, int columns, int hgap, int vgap)

This version of the constructor is called by the previous one. It creates a VariableGridLayout with the specified number of rows and columns, a horizontal gap of hgap, and a vertical gap of vgap. The gaps specify in pixels the space between adjacent components in the horizontal and vertical directions. It is possible to have negative gaps if you want components to overlap. You cannot specify zero for the number of rows or columns. If either rows or columns is zero, the constructor throws the run-time exception NullPointerException.

Support methods

The distinguishing feature of a VariableGridLayout is that you can tell a particular row or column to take up a certain fraction of the display. By default, the horizontal space available is split evenly among the grid's columns; vertical space is split evenly among the rows. This group of methods lets you find out how much space is allotted to each row or column and lets you change that allocation. The sum of the fractional amounts for each direction should add up to one. If greater than one, part of the display will be drawn offscreen. If less than one, additional screen real estate will be unused.

public void setRowFraction (int rowNumber, double fraction)

This method sets the percentage of space available for row rowNumber to fraction.

public void setColFraction (int colNumber, double fraction)

This method sets the percentage of space available for column colNumber to fraction.

public double getRowFraction (int rowNumber)

This method returns the current fractional setting for row rowNumber.

public double getColFraction (int colNumber)

This method returns the current fractional setting for column colNumber.

LayoutManager methods

The only method from GridLayout that is overridden is the layoutContainer() method.

public void layoutContainer (Container target)

The layoutContainer() method draws target's components on the screen in a series of rows and columns. The size of each component within a VariableGridLayout is determined by the RowFraction and ColFraction settings for its row and column.

Miscellaneous methods

public String toString ()

The toString() method of VariableGridLayout returns a string with the current horizontal and vertical gap settings, the number of rows and columns, and the row and column fractional amounts. For example, the string produced by Figure 7.19 would be:

sun.awt.VariableGridLayout[hgap=0,vgap=0,rows=3,cols=3,
    rowFracs=[3]<0.50><0.25><0.25>,colFracs=[3]<0.50><0.25><0.25>]

OrientableFlowLayout

The OrientableFlowLayout is available for those who want something like a FlowLayout that lets you arrange components from top to bottom. Figure 7.19 shows OrientableFlowLayout in use.

Constants

Since OrientableFlowLayout subclasses FlowLayout, the FlowLayout constants of LEFT, RIGHT, and CENTER are still available.

public static final int HORIZONTAL (New)

The HORIZONTAL constant tells the layout manager to arrange components from left to right, like the FlowLayout manager.

public static final int VERTICAL (New)

The VERTICAL constant tells the layout manager to arrange components from top to bottom.

public static final int TOP (New)

The TOP constant tells the layout manager to align the first component at the top of the screen (top justification).

public static final int BOTTOM (New)

The BOTTOM constant tells the layout manager to align the first component at the bottom of the screen (bottom justification).

Constructors

public OrientableFlowLayout () (New)

This constructor creates a OrientableFlowLayout that acts like the default FlowLayout. The objects flow from left to right and have an hgap and vgap of 5.

public OrientableFlowLayout (int direction) (New)

This constructor creates a OrientableFlowLayout in the given direction. Valid values are OrientableFlowLayout.HORIZONTAL or OrientableFlowLayout.VERTICAL.

public OrientableFlowLayout (int direction, int horizAlignment, int vertAlignment) (New)

This constructor creates a OrientableFlowLayout in the given direction. Valid values are OrientableFlowLayout.HORIZONTAL or OrientableFlowLayout.VERTICAL. horizAlignment provides the horizontal alignment setting. vertAlignment provides a vertical alignment setting; it may be OrientableFlowLayout.TOP, FlowLayout.CENTER, or OrientableFlowLayout.BOTTOM. If direction is HORIZONTAL, the vertical alignment is ignored. If direction is VERTICAL, the horizontal alignment is ignored.

public OrientableFlowLayout (int direction, int horizAlignment, int vertAlignment, int horizHgap, int horizVgap, int vertHgap, int vertVgap) (New)

The final constructor adds separate horizontal and vertical gaps to the settings of OrientableFlowLayout. The horizHgap and horizVgap parameters are the gaps when horizontally aligned. The vertHgap and vertVgap parameters are the gaps when vertically aligned.

LayoutManager methods

public Dimension preferredLayoutSize (Container target) (New)

The preferredLayoutSize() method of OrientableFlowLayout calculates the preferred dimensions for the target container. The OrientableFlowLayout computes the preferred size by placing all the components in one row or column, depending upon the current orientation, and adding their individual preferred sizes along with gaps and insets.

public Dimension minimumLayoutSize (Container target) (New)

The minimumLayoutSize() method of OrientableFlowLayout calculates the minimum dimensions for the container by adding up the sizes of the components. The OrientableFlowLayout computes the minimum size by placing all the components in one row or column, depending upon the current orientation, and adding their individual minimum sizes along with gaps and insets.

public void layoutContainer (Container target) (New)

The layoutContainer() method draws target's Components on the screen, starting with the first row or column of the display, and going from left to right across the screen, or from top to bottom, based on the current orientation. When it reaches the margin of the container, it skips to the next row or column and continues drawing additional components.

Miscellaneous methods

public void orientHorizontally () (New)

The orientHorizontally() method allows you to change the orientation of the LayoutManager to horizontal. The container must be validated before you see the effect of the change.

public void orientVertically () (New)

The orientVertically() method allows you to change the orientation of the LayoutManager to vertical. The container must be validated before you see the effect of the change.

public String toString () (New)

The toString() method of OrientableFlowLayout returns a string with the current orientation setting, along with the entire FlowLayout.toString() results. For example:

sun.awt.OrientableFlowLayout[orientation=vertical, 
sun.awt.OrientableFlowLayout[hgap=5,vgap=5,align=center]]


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