Basics of GUI Programming Chapter 11 and Chapter 22

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

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

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

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

Classification of GUI classes Container classes Component classes Helper classes

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

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

GUI Component Classes JButton JTextField JTextArea JComboBox JList JRadioButton JMenu

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

GUI Helper Classes LayoutManager – Interface that specifies how components are arranged in a container

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

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

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

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

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

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)

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); }

MyFrame output

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);

Adding Components - JLabel JLabel – uneditable text 1. Constructors public JLabel() public JLabel (String text) public JLabel (Icon icon) public JLabel (String text, Icon icon, int horizontalAlignment) 2. setIcon(Icon b) Image b = new ImageIcon (“cat.gif”); – Label1.setIcon(b);

Adding Components - JLabel 1..setHorizontalPosition (SwingConstants.CENTER); 2..setVerticalTextPosition (SwingConstants.BOTTOM); 3..setToolTipText(“This is a label”);

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

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.

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); }

Output (using FlowLayout)

The GuessGame file GuessGame.java

End (Part 1) JFrame FlowLayout BorderLayout