1. Ch 20
Layout Management and Event
Handling

2. Layout Managers
 Removes repetitious need to lay out
components precisely.
 Insulates developer from the fact that
components have different sizes when
instantiated on different platforms.
 All implement java.awt.LayoutManager
interface.

3. Layout of Components
 FlowLayout
 left to right & top
down
 BorderLayout
 north, south,
west, east &
center
 CardLayout
 stack of panels
 GridLayout
 tabular form
(rows &
columns)
 GridBagLayout
 tabular
form(variable
row heights and
column widths)

4. Component Size and Position
 Sizes and positions are merely suggestions,
overridden by the LayoutManager.
 Each Component has a preferred size, which
is “just big enough” to display the component.

5. Use Layout Managers
 Default layout managers
 Windows (Frames & Dialogs)
 BorderLayout
 Panels & Applets
 FlowLayout
setLayout(new FlowLayout());
setLayout(new BorderLayout());
setLayout(new CardLayout(());
setLayout(new
GridLayout(rows,columns,xgap,ygap));

6.  FlowLayout
 The flow layout is the default layout manager for all
Panel objects and applets.
 It simply lays out components in a single row, from
left to right starting a new row if its container is not
sufficiently wide .
 Default alignment is CENTER.
 new FlowLayout() // default is centered with 5 pixel
gaps
 new FlowLayout(int align)
 new FlowLayout(int align, int hgap, int vgap)

7. GridLayout
 GridLayout lays out components in a rectangular grid,
where all cells are equal size.
 Components are addes cell by cell left to right ,filling
top row and then moving down
 GridLayout()
default of one column per component, in a single row.
 GridLayout(int rows, int cols)
Creates a grid layout with the specified number
of rows and columns.
 GridLayout(int rows, int cols, int hgap, int vgap)
Creates a grid layout with the specified number
of rows and columns.
 e.g setLayout(new GridLayout(3,5,10,15));

8. BorderLayout
 Divides the container into five regions: east,
south, west, north, and center.
 Takes maximum 5 components only, one per
region.
 Resizes each component to match the size of
its region.
 Resizes each region when the container is
resized.

9. BorderLayout Manager
“Center”
“North”
“South”
“West” “East”

10.  While adding a component a region is
specified as an argument to add()
as BorderLayout.NORTH
 e.g add(new
Button(“OK”),BorderLayout.SOUTH);

11. GridBagLayout
 GridBagLayout is a flexible layout manager
that aligns components vertically and
horizontally, without requiring that the
components be the same size .
 GridBagLayout (int gridx , int gridy, int
gridwidth ,int gridheight ,int weightx,
double weighty double anchor, int fill ,int
insets , int ipadx int ipady )

12.  gridx,gridy : define col ,and row position of upper left
corner.
 gridwidth ,gridheight : no of cells occupied by
components .default is 1 for both
 weightx,weighty: Specifies how to distribute extra
horizontal space
 anchor:It determines where, within the display area,
to place the component.
 fill:This field is used when the component's display
area is larger than the component's requested size.
 Insets:This field specifies the external padding of the
component, the minimum amount of space between
the component and the edges of its display area.
 Ipadx, ipady:This field specifies the internal padding

13.  CardLayout:The CardLayout class lets you
implement an area that contains different
components at different times .
 CardLayout()
Creates a new card layout with gaps of
size zero .
 CardLayout(int hgap, int vgap)
Creates a new card layout with the
specified horizontal and vertical gaps.