1/23: Java Modular Components Identifiers: naming requirements for Java variables & objects Stepping out of the MS-DOS window: The Java Modular Component: the JOptionPane.

Identifiers: How to Name. Must start with a lowercase non-number –but classes must start with a capitalized non-number Can contain alphas (letters), numbers, underscores, dollar signs –acceptable: $dinero value$2 g my_debt Cannot contain other symbols or spaces –unacceptable: a*b Value2 2nd my Cannot be a Java keyword –EX: static void class private import

Outside the MS-DOS Window Most programs today work in a “Windows”-type environment, not a MS-DOS window. Dialog boxes: informational, request input, show output, give warnings, etc. In Java, we use the JOptionPane.

Welcome4.java // Fig. 2.6: Welcome4.java (pg. 66) //Java extension packages – import JOptionPane import javax.swing.JOptionPane; public class Welcome4 { //main method begins execution of app public static void main ( String args[] ) { JOptionPane.showMessageDialog ( null, “Welcome\nto\nJava\nProgramming!” ); System.exit ( 0 ); } comments import statement class header method header statement

JOptionPane: A Dialog Box must import javax.swing.JOptionPane before defining the class. –a library of objects & methods for dialog boxes Usage: a statement like this: JOptionPane.showMessageDialog( null,“Words” ); to get

JOptionPane: Variations The third parameter varies the title bar string: JOptionPane.showMessageDialog ( null, “Words”, “Title Here”, JOptionPane.INFORMATION_MESSAGE) –Replaces the Message header with Title Here. More info available at Title Here

JOptionPane: Variations The last parameter varies the icon shown in the box: JOptionPane.showMessageDialog( null,“Word”,“Title”, … JOptionPane.PLAIN_MESSAGE –JOptionPane.ERROR_MESSAGE –JOptionPane.INFORMATION_MESSAGE –JOptionPane.WARNING_MESSAGE –JOptionPane.QUESTION_MESSAGE More info available at

JOptionPane.showInputDialog A dialog box that allows the user to input a String. EX: JOptionPane.showInputDialog ( “Please type your name” ); Learn more at

Program of the Day: pg. 69 Pg. 69: Addition.java –Pay attention to the use of the dialog boxes. Friday: –Finish Addition.java –Getting comfortable with Dialog Boxes Monday: –Addition.java in depth –Getting values from the user –Strings vs. integers and other primitive data types –Arithmetic operators