1. Object-Oriented Software Engineering
JFrames with Swing

2. Contents
JFrame
Content Pane
Layout Managers
Java Interfaces
ActionListeners

3. JFrame Any interesting GUI will use the JFrame class.
public class FrameDemo {
private static void createAndShowGUI() {
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame frame = new JFrame("FrameDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel emptyLabel = new JLabel("");
emptyLabel.setPreferredSize(new Dimension(175, 100));
frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);
frame.pack();
frame.setVisible(true); }
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
});

4. JFrame private static void createAndShowGUI() {
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame frame = new JFrame("FrameDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel emptyLabel = new JLabel("");
emptyLabel.setPreferredSize(new Dimension(175, 100));
frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);
frame.pack();
frame.setVisible(true); }

5. JFrame Problem is createAndShowGUI is declared static:
private static void createAndShowGUI()
This has to be, because main has to be static, and can only
reference static methods.
Static methods can not reference any non-static variables.
This includes any reference to a non-static class.

6. JFrame For example, move declaration of frame outside scope
of createAndShowGUI:
private JFrame frame;
private static void createAndShowGUI() {
frame = new JFrame("FrameDemo"); }
$ javac FrameDemo.java
FrameDemo.java:10: non-static variable frame cannot be
referenced from a static context
frame = new JFrame("FrameDemo");

7. Content Pane The menu bar and content pane provide functionality
for a JFrame.

8. Content Pane, JPanel public class MyContents extends JPanel {
public MyContents ( ) {
// put contents of JFrame in this
// non-static constructor method }
private static void createAndShowGUI() {
JFrame frame = new JFrame("Person");
MyContents newContentPane = new MyContents( );
frame.setContentPane(newContentPane);

9. Layout Managers
A JPanel must have a layout manager to control where buttons, icons, text areas etc are to be placed with respect to
each other inside the content pane.
JPanel
LayoutManager
newContentPane *
BorderLayout
{ choice of } *
CardLayout *
FlowLayout *
GridLayout *
GridBagLayout

10. Every content pane is initialized to use a BorderLayout.
BorderLayout has five areas.
These areas are specified by the BorderLayout constants
PAGE_START,
PAGE_END,
LINE_START,
LINE_END,
and CENTER.

11. Code for adding buttons to BorderLayout
JButton button = new JButton("Button 1 (PAGE_START)");
newContentPane.add(button, BorderLayout.PAGE_START);
//Make the center component big, since that's the
//typical usage of BorderLayout.
button = new JButton("Button 2 (CENTER)");
button.setPreferredSize(new Dimension(200, 100));
newContentPane.add(button, BorderLayout.CENTER);
button = new JButton("Button 3 (LINE_START)");
newContentPane.add(button, BorderLayout.LINE_START);
button = new JButton("Long-Named Button 4 (PAGE_END)");
newContentPane.add(button, BorderLayout.PAGE_END);
button = new JButton("5 (LINE_END)");
newContentPane.add(button, BorderLayout.LINE_END);
Code taken from Java tutorial, also on course website.

12. BorderLayout: Note Behaviour of buttons depends on the object to
which it belongs.
In a later lecture we will see that buttons attached to
JToolBar will seem to behave differently when
the JToolBar is then attached to
a BorderLayout within a JFrame!

13. BoxLayout
BoxLayout stacks components either as column or in row.

14. BoxLayout Code
public static void addComponentsToPane(Container pane) {
pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));
addAButton("Button 1", pane);
addAButton("Button 2", pane);
addAButton("Button 3", pane);
addAButton("Long-Named Button 4", pane);
addAButton("5", pane); }
private static void addAButton(String text, Container container) {
JButton button = new JButton(text);
button.setAlignmentX(Component.CENTER_ALIGNMENT);
container.add(button);
Code taken from Java tutorial, also on course website.

15. GridBagLayout
GridBagLayout aligns components by placing them within a grid of cells
Components can span more than one cell.
The rows in the grid can have different heights, and grid columns can have different widths.

16. GridBagLayout Grid (0,0) Grid (0,1) Grid (0,2) Grid (1,0) Grid (1,1)

17. GridBagLayout JButton button; pane.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.fill = GridBagConstraints.HORIZONTAL;
Constraint controls where buttons appear within the GridBagLayout.
Resizing component will cause
horizontal space to be shared
across buttons

18. GridBagLayout button = new JButton("Button 1"); c.gridx = 0;
c.gridy = 0;
pane.add(button, c);
button = new JButton("Button 2");
c.gridx = 1;
button = new JButton("Button 3");
c.gridx = 2;
button = new JButton("Long-Named Button 4");
c.ipady = 40; //make this component tall
c.weightx = 0.0;
c.gridwidth = 3;
c.gridy = 1;

19. GridBagLayout button = new JButton("5");
c.ipady = 0; //reset to default
c.weighty = 1.0; //request any extra vertical space
c.anchor = GridBagConstraints.PAGE_END; //bottom of space
c.insets = new Insets(10,0,0,0); //top padding
c.gridx = 1; //aligned with button 2
c.gridwidth = 2; //2 columns wide
c.gridy = 2; //third row
pane.add(button, c);

20. Event Listeners
For a class to provide interaction it might implement the ActionListener and/or the MouseInputListener interfaces in Java as well as extend JPanel.
«interface»
ActionListener
JPanel
«interface»
MouseInputListener
MyNewClass
JFrame 1
1..*

21. Java Interfaces Interface represents a contract defining a protocol.
An interface is a named collection of method definitions, without implementations. An interface can also declare constants.
An interface cannot implement any methods.
An interface has no constructor.
All interface methods are public.
No static methods allowed.
An interface is not part of the class hierarchy. Unrelated classes can implement the same interface.
A class can implement many interfaces but can have only one superclass.

22. MouseInputListener and ActionListener <<interface>>
void mouseClicked (MouseEvent)
void mouseMoved (MouseEvent)
void mouseExited (MouseEvent)
void mouseReleased (MouseEvent)
void mouseEntered (MouseEvent)
void mousePressed (MouseEvent)
void mouseDragged (MouseEvent)
ActionListener
void actionPerformed(ActionEvent)

23. Handling Events
GUI Components communicate with each other by sending events.
A listener is an object that is notified when an event occurs and can examine the contents of that event to perform some action.
Registers to listen for
particular type of events
GUI Component
Event Listener Object
Event
fired by GUI

24. Handling Events
Any number of objects can register to listen for same type of event
Events are multicast to all objects that are
listening
Event
GUI Component
Event
Event

25. Common Events and their Listeners
<<interface>>
java.util.EventListener
java.awt.AWTEvent
ActionEvent
MouseEvent
<<interface>>
ActionListener
<<interface>>
MouseListener
<<interface>>
MouseMotionListener

26. Listening For Events aSource aListener anEvent register( )
<<create>>
notify(anEvent )
query( )