1. Graphical User Interfaces -- Introduction
Users have become accustomed to using a graphical user interface (GUI) through which they interact with a program
Java provides strong support for building GUIs through the java.awt package
This chapter focuses on:
GUI components
event-driven programming
containers and component hierarchies
layout managers

2. GUI Elements The key elements of a Java graphical user interface are:
GUI components
layout managers
event processing
GUI components, such as text fields and buttons, are the screen elements that a user manipulates with the mouse and keyboard
Layout managers govern how the components appear on the screen
Events signal important user actions, like a mouse click

3. Event-Driven Programming
Programs with GUIs must respond to events, generated by GUI components, that indicate that specific actions have occurred
A special category of classes, called listeners, wait for events to occur
Therefore, a GUI program is composed of:
the code that presents the GUI to the user
the listeners that wait for events to occur
the specific code that is executed when events occur

4. Event-Driven Programming
There is a listener interface defined for each event type
Each listener interface contains the abstract methods required to respond to specific events
A listener class implements a particular listener interface
Listeners are "added" to a particular GUI component
When a component generates an event, the method corresponding to that event is executed in the listener
See CardTest.java

5. The GUI Program Model Listeners Program- GUI specific Handle events
Add listeners
GUI
Program-
specific
Event effects

6. Event Interfaces Multiple listeners can be added to a component
Multiple components can be processed by the same listener
Furthermore, one listener class can implement multiple listener interfaces
Therefore one class can listen for many types of events
See TwoListen.java

7. Containers
A container is a special category of GUI components that group other components
All containers are components, but not all components are containers
An applet is a container
Therefore, buttons, text fields, and other components can be added to an applet to be displayed
Each container has an associated layout manager to control the way components in it are displayed

8. Containers
Some containers must be attached to another graphical surface:
panel
applet
Other containers can be moved independently:
window
frame
dialog
See MyFrame.java, FrameWithPanel.java, ExGui.java

9. Containers
Component
Container
Window
Panel
Dialog
Frame
Applet

10. Component Hierarchies
A GUI is created when containers and other components are put together
The relationships between these components form a component hierarchy
For example, an applet can contain panels which contain other panels which contain buttons, etc.
See Rings_Display.java
Careful design of the component hierarchy is important for visually pleasing and consistent GUIs

11. GUI Components
There are several GUI components that permit specific kinds of user interaction:
labels
text fields
text areas
lists
buttons
scrollbars

12. Labels A label defines a line of text displayed on a GUI
Labels are static in the sense that they cannot be selected or modified by the human user once added to a container
A label is instantiated from the Label class
The Label class contains several constructors and methods for setting up and modifying a label's content and alignment
See SampleLable.java

13. Text Fields and Text Areas
A text field displays a single line of text in a GUI
It can be made editable, and provide a means to get input from the user
A text area is similar, but displays multiple lines of text
They are defined by the TextField and TextArea classes
A text area automatically has scrollbars on its bottom and right sides
See SampleTextField.java, SampleTextArea.java

14. Lists
A list, in the Java GUI sense, is used to display a list selectable strings
A list component can contain any number of strings and can be instantiated to allow multiple selections within it
The size of the list is specified by the number of visible rows or strings within it
A scrollbar will automatically appear on the right side of a list if the number of items exceed the visible area
See SampleList.java

15. Buttons The java.awt package supports four distinct types of buttons:
Push buttons
Choice Buttons
Checkbox buttons
Radio buttons
Each button type serves a particular purpose
See SampleButton.java

16. Choice button
A choice button is a single button which displays a list of choices when pushed
The user can then scroll through and choose the appropriate option
The current choice is displayed next to the choice button
It is defined by the Choice class
See SampleChoice.java

17. Checkbox button A checkbox button can be toggled on or off
A set of checkbox buttons are often used to define a set of options as a group, though one can be used by itself
If used in a group, more than one option can be chosen at any one time
Defined by the Checkbox class
See SampleCheckBox.java

18. Radio buttons
A radio button, like a checkbox button, is toggled on or off
Radio buttons must be grouped into a set, and only one button can be selected at any one time
When one button of a group is selected, the currently selected button in that group is automatically reset
They are used to select among a set of mutually exclusive options
See SampleRadioButtons.java

19. Scrollbars
A scrollbar is a slider that indicates a relative position or quantity
They are automatic on text areas and list components, but can be used independently
The position of the slider in the range corresponds to a particular numeric value in a range associated with the scrollbar
A scrollbar is defined by the Scrollbar class
See Zoom.java

20. Layout Managers
There are five predefined layout managers in the java.awt package:
flow layout
border layout
card layout
grid layout
Each container has a particular layout manager associated with it by default
A programmer can also create custom layout managers

21. Flow Layout
Components are placed in a row from left to right in the order in which they are added
A new row is started when no more components can fit in the current row
The components are centered in each row by default
The programmer can specify the size of both the vertical and horizontal gaps between the components
Flow layout is the default layout for panels and applets
See Flow.java

22. Grid Layout
Components are placed in a grid with a user-specified number of columns and rows
Each component occupies exactly one grid cell
Grid cells are filled left to right and top to bottom
All cells in the grid are the same size
See Grid.java

23. Border Layout
Defines five locations each of which a component or components can be added
North, South, East, West, and Center
The programmer specifies the area in which a component should appear
The relative dimensions of the areas are governed by the size of the components added to them
See Border.java

24. Border Layout
North
West
Center
East
South

25. Card Layout
Components governed by a card layout are "stacked" such that only one component is displayed on the screen at any one time
Components are ordered according to the order in which they were added to the container
Methods control which component is currently visible in the container
See Card.java

26. GUI Design
Careful design of a graphical user interface is key to a viable software system
To the user, the user interface is the system
For each situation, consider which components are best suited and how they should best be arranged
See Quotes.java