CS591x

1. CS591x A very brief introduction to Java

2. Java • Java • Developed by Sun Microsystems • was intended a language for embedded applications • became a general purpose language • designed to support network programming

3. Java • Java is a semi-compiled language • Java compiler produces bytecode • Bytecode not executable by itself like a binary executable (… except…) • Must run Java bytecode in an execution environment • Java Virtual Machine – JVM • This give Java programs portability

4. Java • Must download and install Java Software Developers Kit (SDK) • A lot of kinds of Java out there • You want J2SE 1.4.2 SDK • Download it from java.sun.com • install • You may want a Java IDE

5. Java - Installation • Installation should be straight-forward • download • open the installer package • see installation instructions on java.sun.com/j2se • Follow installation instructions/answer questions

6. Java • Java SDK comes with a number of tools • Java compiler • javac myprogram.java • compiler produces class files • Java runtime environment (JVM) • java myprog • Java Archiver – jar • jar cvf myjar.jar myprog.class ….

7. Java – Basic Syntax public class myprog { public static void main(String[] args) { System.out.println(“Hello from myprog”); } }

8. Java – Basic syntax • a Java program must start with a class name • class name must match the program’s file name • compiler will produce a .class file with the same name

9. Java – Basic syntax • Java programs contain classes and methods • There are Java applications and Java applets • A Java application must have a main method public static void main(String[] args){ … }

10. Java – Basic Syntax • Classes have zero or more properties and zero or more methods • properties are variables associated with class • methods are procedures for operating on the class, objects or properties • Objects are instances of classes

11. Java – sample program public class sample { public static void main(String[] args) { String str; str = “first string”; System.out.println(str); str = “2nd string”; System.out.println(str); } }

12. Java Data Types • chr – single unicode character • String – string of characters • int – integer • float – floating point number • boolean – boolean value

13. Java – Data Types • byte – single byte signed integer • short – two byte signed integer • long – very double precision integer • double – double precision float

14. Java • Arithmetic operators • + - * / % ++ -- • use parentheses to set precedence • Logical operators • && - logical AND || logical OR ! logical NOT • Assignment int x = 12; String st = “Hello”; float a = 12.5; a=b; a+=b; a-=b; a*=b; a/=b; a%=b; • Comparison operators • == != > < >= <=

15. Java Statements if (comparison-op) { code to be exec;} if (comparison-op) {do_this_code;} else {do_this_code_instead;} switch(num) { case 1 : {do_this;} case 2 : {do_that;} case 3 : {do_the_other;}

16. Java Statements for (initial_val; exit_test; increment) {iterative_code;} works just like c while (test_cond) { do_this_code;} do {do_this_code;} while (test_cond);

17. Java - Statements break; breaks out of a loop if (x==3) break; continue; drops through a loop if (x==3) continue; labels bigloop: for… continue bigloop;

18. Java Statements return – returns to the calling method can return values from called methods

19. Java - statements Arrays int[] x = {4,5,6}; String[] days = {“Monday”,”Tuesday”,…};