1. Java GUI

2. Structure of a GUI App A GUI app consists of a frame controls code
This app is made of:
Frame – window
Controls – such as buttons and labels
Properties – such as size, color
Methods – built in procedures related to properties
Event Methods – such as clicking
General Methods – code not related to objects

3. Steps in Building a GUI Create the frame.
Create the user interface by placing controls on the frame.
Write code for control event methods, and perhaps other methods.
We will use the java Swing and AWT components, so
import javax.swing.*;
import java.awt.*;

4. Testing
The event-driven nature of Java allows you to build your app in stages and test it at each stage. Build one method, or part of a method, and get it working before moving on. This minimizes errors and increases your confidence. Build a little, test a little, modify a little, and test again!

5. Swing Controls These all have names beginning with J JFrame JButton
basic container for other controls
title property establishes caption
JButton
used to start some action
text property establishes the caption
JLabel
allows placement of formatted text on a frame
text property establishes the caption

6. Swing Controls, continued
JTextField
accepts a single line of typed information
JTextArea
accepts multiple lines of scrollable typed info
JCheckBox
provides yes or no answer
JRadioButton
allows selection from a mutually exclusive group
JComboBox
users can choose from a drop down list

7. Swing Controls, continued
JList
like a combo box with the list always visible
allows multiple selections
JScroll
a scroll bar control used to select from a range of values
always buddied with another related control

8. Creating a Frame This is the first step in building a GUI app
The following is an example from the Stopwatch project

9. Extending the JFrame means that this Stopwatch object takes on all characteristics of such a frame.
This is the constructor. It has the same name as the class. It is called from the main method.
These are methods.

10. User Interface
Once the frame is created, we ‘place’ controls in the frame. The layout manager determines how controls are arranged. There are several to choose from. The GridBagLayout offers a nice interface appearance by placing controls into a rectangular frame like a table or a 2D array.

11. User Interface, cont. A frame contains several panes.
Controls are placed into the content pane.
The GridBagLayout manager divides the content pane into rows and columns.

12. Placing a Control into a GridBag Layout
Declare the control
Create the control
Set the desired control properties
Add the control to the desired position
We will declare all the controls with class level scope so that any method in the class may use them.

13. JButton startButton = new JButton();
Adding Controls
Declare the control
ControlType controlName;
For ex, JButton startButton;
Create the control
controlName = new ControlType();
For ex, startButton = new JButton();
You may combine steps 1 & 2:
JButton startButton = new JButton();

14. startButton.setText(“Start Timing”);
Adding Controls, cont.
Set the desired control properties
controlName.setPropertyName(PropertyValue);
For ex,
startButton.setText(“Start Timing”);

15. Adding Controls, cont. Add the control to the desired position
Declare a GridBagConstraints object to allow position
GridBagConstraints gridConstraints = new GridBagConstraints();
Choose x and y location.
gridConstraints.gridx =0;
gridConstraints.gridy=0;
Add the control.
getContentPane().add(controlName,gridConstraints);
For ex,
getContentPane().add(startButton,gridConstraints);

16. Adding Controls, cont.
To finalize placement of controls in the frame, execute a pack method. pack(); This “packs” the grid layout onto the frame and makes the controls visible.

17. Stopwatch Project Complete the Stopwatch project GUI from
Learn Java (GUI Applications), Chapter 1.
pages 1-29 to 1-35
pages 1-44 to 1-50

18. Event Methods
The next step is to add code in event methods and their corresponding listeners. There are two ways…one for AWT and one for Swing objects. Listeners are added into the frame constructor code.

19. AWT Event Listeners
Event listeners for AWT objects are implemented using adapters. Every project needs to “listen” for the event when the user closes the window. Add this code to the frame constructor.

20. Swing Event Listeners
actionPerformed event methods are added using ActionListener.

21. controlNameActionPerformed
We could add the code for the action to the listener, but it is cleaner to add it in an external method as shown here:
This makes editing, modifying, and testing easier.

22. Stopwatch, cont. Complete the Stopwatch project GUI from
Learn Java (GUI Applications), Chapter 1.
pages 1-62 to 1-64
Try the options on page 1-69
Savings Account Project, Learn Java (GUI App)
p 2-28 to 2-35