PROGRAMMING REVIEW Lab 2 EECS 448 Dr Fengjun Li and Meenakshi Mishra

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

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

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

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

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

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

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

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

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 { //…}

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();

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) { //..}

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