Programming Review

1. Programming Review Lab 2 EECS 448 DrFengjun Li and Meenakshi Mishra

2. Software Development • Science or Art? • Science • Parts of it have fixed objective which must be met • Building new technology to help mankind • Art • Most clients just give a rough idea what they want • The final product is result of programmer’s imaginations • The more you practice, the better you get at it • There are basic techniques that can be taught; other than that you are on your own

3. Task for Today • Build a java application for a basic calculator • The user selects the basic operations from drop-down menu • The options should be addition, subtraction, multiplication, devision • The user enters the numbers in two text fields provided • The result appears in third text field

4. A tip that always helps • Approach the problem in small steps • Breaking the problem down in steps helps debugging • For example in this case • First write an application just to launch the application window • Change your program to include the textfields and labels • Write a code to just do addition • Plug in the drop-down menu and adjust the program accordingly

5. Working with swing • A package written for developing sophisticated GUI • Adopts style of the operating system or style unique to Java • Each style is called look and feel • Java 7 introduces new look and feel called Nimbus, that is unique to Java • Must avail the swing package first • import javax.swing.*; • Other packages supporting GUI programming • java.awt (Abstract Windowing Toolkit) • java.awt.event (class handling user input) • Swing generally more powerful than awt • Not implemented by platform specific code, but written entirely in java • Supplies plenty of exciting additions like scroll panes, trees, tables etc • When using Swing component, you work with object of that Swing class • All Swing components are subclasses of abstract class JComponent

6. Creating Interface • Create a class that represents the main GUI • In most projects, main interface is a frame (JFrame class) • Frame is a window that appears whenever you open an application • Frame has a title bar, Maximize, Minimize, Close buttons and other features • Users of graphical environments expect to move, resize and close the windows • To create a graphical Java application, make the interface a subclass of JFrame • public class MyFirstGui extends Jframe • Set title by either setTitle(String) or super(String) in the constructor • Set size by setSize(int, int) where first number denotes width and second height in pixels • Make your frame visible by setVisible(true); • Set default close operation to exit on closing setDefaultCloseOption(EXIT_ON_CLOSE) • Other close options • DISPOSE_ON_CLOSE • HIDE_ON_CLOSE • DO_NOTHING_ON CLOSE

7. Adding Components • Class JButton • Three constructors • JButton(String) Label on the button • JButton(Icon) Icon on the button • JButton(String,Icon) Both icon and Label on the button • JButton b = new JButton(“OK”); • Class JPanel • After creating components, need to add them to a container • Simplest container • JPanel p = new JPanel(); • p.add(b); //add button b to panel p

8. Adding Components • Class JTextField • JTextField() Empty Text field • JTextField(int)  Text Field with specified width • JTextField(String, int)  Text Field with specified width and text • setEditable(False) for text fields that do not accept user input • Class JLabel • Three Constructors • JLabel(String) Label with specified text • JLabel(String, int)  Label with specified text and alignment • SwingConstants.LEFT • SwingConstants.RIGHT • SwingConstants.CENTER • JLabel(String, Icon, int) Label with specified text, icon and alignment

9. Adding Components • Class JComboBox • Creates a list of items that are hidden when menu is not being used • addItem(Object) Add item to the list • getItemAt(int)  Returns the text of the list item at specified index position • getSelectedIndex()  Returns the index position of selected item • getSelectedItem()  Returns the text of currently selected item • setSelectedIndex(int)  Selects the item at indicated index position • setSelectedIndex(object)  Selects specified object in the list

10. Responding to User Inputs • Use java.awt.event package • Useful listener interfaces • ActionListener When user performs an action on a component. • AdjustmentListener When component is adjusted • FocusListener Textfield or area loses or gains focus • ItemListener When items in items such as combo box are changed • KeyListener When user enters text using keyboard • MouseListener Generated by mouse clicks, mouse entering or leaving a component area • MouseMotionListener track all movement by mouse over component • WindowListener When window is minimized, maximized, moved or closes • Implement listener in class definition • public class t extends JFrame implements ActionListener, ItemListener { //…}

11. Setting up Components • Need to add the attribute of listening to specific objects • addActionListener()  JButton, JCheckBox, JComboBox, JTextField, JRadioButton and JMenuItem • addFocusListener()  all Swing Component • addItemListener()  JButton, JCheckBox, JComboBox and JRadioButton • addKeyListener()  all Swing Components • addMouseListener()  all Swing Components • addMouseMotionListener()  all Swing Components • addTextListener()  JTextField and JTextArea • addWindowListener()  JWindow and JFrame • JButton b = new JButton(‘OK”); • b.addActionListener();

12. Event Handling Methods • Action Events • ActionListener actionPerformed(ActionEvent) • Focus Events • FocustListener focusGained(FocusEvent) and focusLost(FocusEvent) • Item Events • ItemListener itemStateChanged(ItemEvent) • When a class implements an event interface, must define the corresponding event handling methods • public void actionPerformed(ActionEvent e) { //..} • To know which for which object the event was generated • Object source=e.getSource(); • If the event was triggered by button b, you can check using if (source==b) { //..}

13. Summary of designing application • Import packages • Create a Class that extends JFrame and implements all the user interfaces required • Make sure to set the frame to visible, set title, declare size, the application exits on closing • Create the components • Add property of user input listening to the components • Add the components to a simple container (optional) • Add the container to the Frame • Define what to do when the user enters required input • Define event handling methods