COMP 14 Introduction to Programming Adrian Ilie July 21 2005 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Last Time Create a Java window extending JFrame Add labels with JLabel Add Images with ImageIcon Setting colors and layout 2 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Example LowerUpperCase 3 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Basics Layout GridLayout 3 2 JLabel to output result JTextField to input sentence 4 buttons 4 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL JLabel and JTextField Very similar With JTextField we can also type data from outside and access it in the program JLabel output new JLabel JTextField input new JTextField String inputStr input getText output setText OUTPUT RESULT 5 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Using Buttons Create JButton objects Buttons generate events when clicked Add event handlers Inside event handler code operations to be executed when button is clicked 6 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Adding Buttons To create a button we use the JButton class JButton toLower new JButton To Lower Case Add button to the content pane content add toLower Change text of the button with the setText method toLower setText Convert to Lower Case Enable disable the button with setEnabled method toLower setEnabled false 7 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Buttons and Events Pressing buttons triggers action events Setup a listener for the event actionPerformed method from ActionListener class ActionListener class from the java awt event package something else to import 8 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ActionListener Special type of class called interface Interface class that contains only the method headings no method bodies public interface ActionListener public void actionPerformed ActionEvent e 9 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ActionListener In order to handle an event define a class that will implement ActionListener private class ButtonHandler implements ActionListener Make the class ButtonHandler an internal class of our main class In ButtonHandler code the method actionPerformed 10 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ActionListener Declare a ButtonHandler that will be a data member of the main class private ButtonHandler toLowerHandler Instantiate the ButtonHandler e g in the constructor toLowerHandler new ButtonHandler Once the JButton object is created register the action listener toLower addActionListener toLowerHandler 11 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Example LowerUpperCase Declare buttons toLowerButton toUpperButton exitButton clearButton Instantiate buttons Add buttons to the content pane Implement ActionListener classes that will handle events ButtonHandler ExitHandler ClearHandler Register action listeners 12 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL actionPerformed Variables we want to access inside the actionPerformed methods must be declared as member variables of the main class not local to constructor Make input output and the buttons member variables 13 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ExitHandler actionPerforme d We simply need to exit the system System exit 0 14 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ClearHandler actionPerform ed Clear JTextField input and JLabel output input setText output setText setVisible true 15 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL ButtonHandler actionPerforme d How do we know which button we pressed toLower or toUpper public void actionPerformed ActionEvent e JButton pressed JButton e getSource if pressed toLower else if pressed toUpper 16 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Example LowerUpperCase Finish example 17 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Applets A Java application is a stand alone program with a main method A Java applet is a Java program that is intended to be transported over the web and executed using a web browser an applet doesn t have a main method needs an extra import statement import java applet Applet 18 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Applet Methods Several methods from Applet class that are invoked automatically at certain points in an applet s life init executed only once when the applet is initially loaded start called when applet becomes active when browser loads returns to the page stop called when applet becomes inactive when browser leaves the page paint automatically executed and is used to draw the applets contents 19 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Converting Apps to Applet See Ch 13 pgs 855 858 745 748 Extends JApplet instead of JFrame No main method No constructor put code from constructor in init method No setVisible setTitle or setSize methods 20 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Example LowerUpperCase Convert to Applet 21 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Want to Learn More Creating a GUI with Swing http java sun com docs books tutorial uiswing Creating Applets http java sun com docs books tutorial applet 22 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Writing Web Pages Web pages are written in a markup language called HTML HyperText Markup Language HTML is NOT a programming language HTML just tells the computer how to format text and images it s like using Word but having to type in what you want things to look like 23 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Tags HTML works based on the concept of tags A tag is some text surrounded by and Tags are not printed to the screen Example tags HTML TITLE P H1 A lot of the time they work in pairs HTML and HTML HTML is not case sensitive HTML and html are the same thing 24 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Very Simple Web Page HTML HEAD TITLE Simple web page TITLE HEAD BODY This is the text on a web page BODY HTML View any web page source 25 Adrian Ilie by choosing Source from the View menu in a web browser The UNIVERSITY of NORTH CAROLINA at CHAPEL What Do The Tags Mean HTML HTML go at the beginning and end of EVERY page HEAD HEAD introduction of the document TITLE TITLE what goes in the title bar of the window BODY BODY the text and other stuff that is displayed in the window 26 Adrian Ilie The UNIVERSITY of NORTH CAROLINA at CHAPEL Color and Images You can add color or an image to the