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Creating True Executables • In order for the JVM to run your program, it needs to know where to start. main and Scanner • Put public static void in one of your classes. main(String[] args){ } • Implement this method to create the objects and call the methods in order to run the program. NSCC CSC 142 Notes Winter 2005 l-1 NSCC CSC 142 Notes Winter 2005 Running your program l-2 Simple Text Input • Via the GUI interface (e.g. Windows) • Scanner class – Create a .jar file – Specify which class has the main method to use as the starting point – double click on the .jar icon – Used to read in data to a program – Either from the keyboard (System.in), a file, or other stream – Easily parses the stream into primitives and String data – Part of the java.util package • From the command line – Start the JVM and specify the name of the class that has the main method EX: I:\> java PointProgram • For help in running executables http://java.sun.com/docs/books/tutorial/getStarted/cupojava/ind ex.html NSCC CSC 142 Notes Winter 2005 l-3 NSCC What is a package? CSC 142 Notes Winter 2005 l-4 import To use a class that is in a package, you must use its complete name (e.g. java.util.Scanner) The import statement allows you to refer to a class by its simple name. (e.g. Scanner) • Because the Java language has so many classes (> 2500) they are organized into packages. import java.util.*; • Helps to avoid name collisions (2 classes with the same name). They reside in separate packages. public class Test{ public class Test{ public Test(){ public Test( ){ java.util.Scanner c = newjava.util.Scanner(…); Scanner c = new Scanner(…); } } } } NSCC CSC 142 Notes Winter 2005 l-5 NSCC CSC 142 Notes Winter 2005 l-6 1 import (cont.) Back to the Scanner class You can either import a single class import java.util.Scanner; • To create the Scanner object for keyboard input Scanner in = new Scanner(System.in); Or the entire package import java.util.*; • Class contains methods for reading in data – nextXxx() where Xxx is a numeric type. – next() to read in the next String. – See the class API to learn about others. Careful when importing entire packages. May still have naming collisions. NSCC CSC 142 Notes Winter 2005 l-7 NSCC CSC 142 Notes Winter 2005 l-8 2