1. Java Swing - Lecture 3 Layout Management
Boriana Koleva

2. Where are we up to? Last Time: Today Containers (Frames and Dialogs)
Hierarchy
Root Panes
Layered Panes
Content Panes
Glass Panes
Components
Lots of ‘em…
Today
The exciting topic of “Layout Management”
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3. Laying out components Manage realized components
Determine size and position
Each container has a layout manager
(usually)
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4. Layout managers – general aspects
Creating a layout manager
Consulting managers
Types of managers
Choosing managers
Other features of component layout
All Covered very well here:
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5. Creating a layout manager
Default layout managers
JFrame, JDialog, JApplet have BorderLayout
JPanel has FlowLayout
Except when used as a Content Pane (Border Layout)
Setting the layout manager for a container
JFrame frame = new JFrame();
frame.setLayout(new FlowLayout());
JPanel contentPane = new JPanel();
contentPane.setLayout(new BorderLayout());
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6. Consulting layout managers (1)
Consulted automatically when container may need to change its appearance.
These methods result in consultation, but DON’T trigger new layout
add(), remove(), removeAll()
getAlignmentX(), getAlignmentY()
getPreferredSize(), getMinimumSize(), getMaximumSize()
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7. Consulting layout managers (2)
These methods actually result in the manager performing layout.
JFrame.pack();
Causes this Window to be sized to fit the preferred size and layouts of its subcomponents.
JFrame.show() & JFrame.setVisible(true);
Shows the component
JComponent.revalidate();
This method will automatically be called on this component when a property value changes. Looks for all dependent components and calls validate() on them. Validate() causes a container to lay out its subcomponents again
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8. Layout managers - types
BorderLayout
BoxLayout
FlowLayout
GridLayout
GridBagLayout
CardLayout
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9. BorderLayout Setting gaps between components (default = 0) Five areas
NORTH, SOUTH, EAST, WEST and CENTER
Not all areas must be used
Do not assume a default area for components
Centre gets as much area as possible
Specify location as argument of add method
pane.setLayout(new BorderLayout());
pane.add(new JButton(“Button 1 (NORTH)”), BorderLayout.NORTH);
Setting gaps between components (default = 0)
BorderLayout.setHgap(int gap);
BorderLayout.setVgap(int gap);
BorderLayout(int horizontalGap, int verticalGap) - Constructor
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10. BoxLayout (1) Components on top / next to each other
Direction is your choice
Tries to size components at preferred height for Y_AXIS or width for X_AXIS
Width as largest component width
See above picture
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11. BoxLayout (2) Space fillers
Rigid - fixed-size space between two components
Glue - taking up no space unless you pull apart the components that it's sticking to. Helps reposition extra space (default is at end)
Custom - Use this to specify a component with whatever minimum, preferred, and maximum sizes you want
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12. BoxLayout (3) Component sizes Alignment
Respect Max, Min and Preferred Sizes of components
Alignment
Comes into play when not all components are the same width
Can specify Left (0), Centre (0.5) or Right (1). Or Top Middle Bottom
If you are having layout problems, first treat as an Alignment issue, then examine sizes.
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13. FlowLayout Very simple - JPanel’s default Components in row(s)
At preferred size
Alignment
FlowLayout.LEFT
FlowLayout.CENTRE
FlowLayout.RIGHT
Gaps
Default = 5
Specifying - setter hGap vGap methods or via constructor
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14. GridLayout Grid of cells - all same size
Components take all space in a cell
Gaps
default = 5
use setter methods hGap and vGap
or via arguments to constructor
Re-sizing
Cells resize to be as large as possible in given window / container
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15. GridBagLayout (1) Very flexible (and complex!)
Rows can have different heights
Columns can have different lengths
Uses cells in a grid
GridBagLayout gridbag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
JPanel pane = new JPanel();
pane.setLayout(gridbag);
//--- For each component to be added to this container:
// Create the component...
// Set instance variables in the GridBagConstraints instance...
gridbag.setConstraints(theComponent, c);
pane.add(theComponent);
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16. GridBagLayout (2) Constraints Example explained very well here:
set in an instance of a gridBagConstraints Object
gridx and gridy - The row and column of the upper left of the component
Anchor - Where to display within cell when component is smaller than it
fill - How to size component when cell is larger than components requested size
insets - External padding - min space between component and cell edges
ipadx, ipady - Internal padding - What to add to min size of components
weightx and weighty - How to distribute extra space (padding)
gridwidth and gridheight - Number of columns or rows the component uses
More explanation here:
Example explained very well here:
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17. CardLayout Manages objects (usually JPanels) in sets
Works much like tabbed pane
Choose cards by
Asking for card in order added to container
Going backwards or forwards
Specifying card by name
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18. Choosing layout managers (1)
In order to display a component in as much space as it can get, consider:
BorderLayout
Component in centre
GridBagLayout
fill=GridBagConstraints.BOTH
BoxLayout
Component specifies very large preferred/maximum sizes
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19. Choosing layout managers (2)
To display a few components in a compact row:
JPanel’s default FlowLayout
BoxLayout
Display a few components of the same size in rows and columns
GridLayout
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20. Choosing layout managers (3)
Display a few components in a row or column, with different spacing between them and custom component sizes
BoxLayout
Display a complex layout that has many components
GridBagLayout
Using JPanel grouping and hierarchies
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21. Layout managers - other layout features
Absolute positioning of components
When
How
Customising layout managers
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22. Absolute positioning (1)
Don’t do it; unless…
component size isn’t affected by container size or font & look’n’feel changes
e.g. desktop panes containing internal frames
custom container performs size & position calculations particular to container
e.g. split panes
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23. Absolute positioning (2)
Key points from NoneWindow.java
Instruct window to use no Layout:
.contentPane.setLayout(null);
Set components size and position with
XYZ.setBounds(x, y, width, height);
Set window size with:
window.setSize(x, y);
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24. Custom layout managers (1)
Ensure no existing manager does the job
GridBagLayout / BoxLayout
Layout manager downloads
If your trying to do it, chances are someone else has done it already…
DECLARE use of external code in coursework
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25. Custom layout managers (2)
Create class which implements Layout Manager interface
e.g. public class myManager implements LayoutManager
Must have 5 methods required by interface
void addLayoutComponent(String, Component)
void removeLayoutComponent(Component)
Dimension preferredLayoutSize(Container)
Dimension minimumLayoutSize(Container)
void layoutContainer(Container)
See below URL for more documentation
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26. Summary Creating a layout manager Consulting managers
Types of managers
BorderLayout GridLayout
BoxLayout GridBagLayout
FlowLayout CardLayout
Choosing managers
Absolute positioning
Custom layout managers
Next time: Event handling and event listeners
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