Basics of GUI Programming

1. Basics of GUI Programming Chapter 11 and Chapter 22

2. GUI Components • GUIs are built from GUI components. • GUI component is an object with which the user interacts via--- • Mouse • Keyboard • Voice • Etc;

3. Simple GUI Input/Output • Java’s JOptionPane in javax.swing • showMessageDialog static method • showInputDialog static method • Used for very simple input and output

4. GUI Components • Two sets of GUI components in Java • Swing (in package javax.swing) • AWT ( in package java.awt) • AWT • components are automatically mapped to the platform-specific components • Tied to the local platform • Prone to platform-specific bugs • Referred to as heavyweight components • Eventually fade away

5. GUI Components • Swing • More robust, versatile, and flexible than AWT components • Less dependent on the target platform • Referred to as lightweight components

6. Classification of GUI classes • Container classes • Component classes • Helper classes

7. Container Classes • Component classes that are used as containers to contain other GUI components • JFrame • Window not contained inside another window • Container that holds other Swing components • JFrame object is a window – has a border, sizing buttons • JPanel • Invisible container that holds user-interface components • Can be used as a canvas to draw graphics • Can be nested • JApplet

8. Java GUI API Object Component Font Graphics Color Container Window JComponent Panel Frame Applet JPanel JApplet JFrame

9. GUI Component Classes • JButton • JTextField • JTextArea • JComboBox • JList • JRadioButton • JMenu

10. GUI Helper Classes • Used by components and containers to draw and place objects • Graphics • Abstract class for drawing strings, lines and simple shapes • Color • Specifies colors of GUI components • Font • Specifies fonts for the text and drawings on GUI components

11. GUI Helper Classes • LayoutManager • Interface that specifies how components are arranged in a container

12. Layout Managers • Java GUI components are placed in containers, where they are arranged by the container’s layout manager. • Layout manager places components in the correct locations in the containers

13. Layout Managers - Examples • FlowLayout – simplest layout manager • Components are arranged in the container from left to right, top to bottom in the order in which they were added • Default manager • BorderLayout • Has 5 regions NORTH (top), SOUTH (bottom), EAST (right side), WEST (left side) and CENTER

14. JFrame methods To create a user interface, you need to create either a frame or an applet to hold user-interface components. • JFrame() – constructs an untitled JFrame object • JFrame(String ) – constructs a JFrame object with the specified title

15. JFrame methods • void setDefaultCloseOperation (int operation) Operation tells the program what to do when the frame is closed. Possible values are: • DO_NOTHING_ON_CLOSE • HIDE_ON_CLOSE • DISPOSE_ON_CLOSE • EXIT_ON_CLOSE

16. JFrame methods • setSize (int width, int height) • Specified in pixels • Defined in Component class • setTitle (String title) • dispose() – eliminates calling frame and all subcomponents • setVisible (boolean value) • Defined in Component class

17. JFrame Concepts • JFrame will display only when setVisible is set to true • If setSize() is not used, frame will be 0x0; nothing will be seen but the title bar. • If setDefaultCloseOperation is not used, the program does not terminate and user must break at the DOS prompt (windows)

18. JFrame Example import javax.swing.JFrame; public class MyFrame { public static void main (String args[]) { JFrame frame = new JFrame (“My Frame”); frame.setSize (400,300); frame.setVisible (true); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); } }

19. MyFrame output

20. JFrame Concepts • JFrame object can have components added • Components must be added to the content pane of the JFrame • Think of a content pane as the “inside” of the JFrame • In Java , you can add components directly to the frame and it automatically adds them to the content pane. • Example: add(component); • Older versions: getContentPane().add (component);

21. Adding Components - JLabel • JLabel – uneditable text • Constructors • public JLabel() • public JLabel (String text) • public JLabel (Icon icon) • public JLabel (String text, Icon icon, int horizontalAlignment) • setIcon(Icon b) • Image b = new ImageIcon (“cat.gif”); • Label1.setIcon(b);

22. Adding Components - JLabel • .setHorizontalPosition (SwingConstants.CENTER); • .setVerticalTextPosition (SwingConstants.BOTTOM); • .setToolTipText(“This is a label”);

23. JTextField • Enables user to enter data from the keyboard • Also can be used to display editable or un-editable text

24. Example Design the GUI for a “guessing” game. User should be asked to guess a number between 1 and 10. Points are deducted each time the user guesses the wrong number.

25. Java application for GuessGame import javax.swing.JFrame; public class TestGuessGame { public static void main (String args[]) { GuessGame aGame = new GuessGame(); aGame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); aGame.setSize (200,200); aGame.setVisible (true); } }

26. Output (using FlowLayout)

27. The GuessGame file GuessGame.java

28. End (Part 1) • JFrame • FlowLayout • BorderLayout