Introduction to Java

1. Introduction to Java Tavaris J. Thomas Ph.D. BNAI ZION SCIENTISTS DIVISIONJOB ORIENTATION & TERMINOLOGY CLASSES Fall 2012

2. Contact Info • Tavaris J. Thomas • tavaris@gmail.com • www.ee.cooper.edu/~tthomas/java • Google Group • http://groups.google.com/group/bz-java

3. Any Programming Experience?

4. Class Logistics • Lectures will run every Tues 6:00pm – 9:00pm • The Cooper Union Microlab 602 • Approx 4+ programming assignments. • Class Lectures will be available on the class group page or on the class webpage • Textbook: • Core Java ,Volume 1 – Fundamentals (8th edition) • Cay S. Horstmann and Gary Cornel • ISBN: 0132354764

5. Course Topics • Introduction to Java • Fundamentals • Objects and Classes • Inheritance • Interfaces and Inner Classes • Deploying Applications • Debugging and Exceptions • Multithreading

6. Week 1 • Introduction • What is Java? • Installing the Java SDK and Eclipse IDE • Language Fundamentals

7. History of Java • Began as a Sun Microsystems project called “Green” • James Gosling • Intended to be used on a variety of architectures • All code is translated to the same “Virtual Machine” code, and specific interpreters are written for the VM • Chose to make it object-oriented like C++ instead of like Pascal • First commercial application: applets (1995)

8. Java’s Evolution • Java 1.0 First release • Java 1.1 Inner classes • Java 1.2-1.3 (no additions) • Java 1.4 Assertions • Java 5.0 [“1.5”] Generic classes, for each loops, variable arguments, autoboxing, metadata, enums, static import • Java 6 Performance improvements, library enhancements update 37 • Java 7 More security and library enhancements – update 9 • Java 8 TDA September 2013

9. Versions of Java • Java SE – Standard Edition • Java ME – Micro Edition – embedded devices or resource constrained devices – set top boxes, blu-ray players, mobile devices • Java EE – Enterprise Edition – For server side processing

10. Uses of Java • “Write Once, Run Anywhere” • Stand alone applications • Applets (java code embedded into webpages run via we browser) • Servlets (server side Java code that interact with clients typically using HTTP) • Android development

11. Programming Languages • Interpreted languages • Perl • Python • PHP • Compiled languages • BASIC • C/C++ • Fortran • Java(to bytecode)

13. JVM Approach • Architecture neutral • Only need an implementation of JVM for the native machine • Same Java code will run on all platforms • Portable • The results on x86 = results on ARM = results on PPC • Caveat: don’t always fully utilize architecture capabilities • Object oriented • Everything is a class • Doesn’t this all mean Java is slow? • On average: slower than compiled languages • But, using just-in-time (JIT) compiler Java is fast!

14. Grabbing Java and Eclipse • Go to http://www.oracle.com/technetwork/java/javase/downloads/index.html • Download Java SE 6Update 37 JDK (includes the JRE) • Install the JDK • Install the JRE • Download Eclipse from: http://www.eclipse.org/downloads/packages/eclipse-ide-java-developers/heliossr2 • Continue with installing Eclipse IDE

15. Hello World Example • Simplest possible program: prints one line • Will re-visit this program later public class HiWorld { public static void main(String[] args) { System.out.println(“Hello World“); } }

16. Another Example • Uses an array of three strings and a loop public class Greetings { public static void main(String[] args) { String[] greeting = new String[3]; greeting[0] = "Welcome to BNAI ZION"; greeting[1] = “Introduction to Java"; greeting[2] = “Spring 2012 "; for(String thisline : greeting) System.out.println(thisline); } }

17. “Hello World” In-depth public class HiWorld { public static void main(String[] args) { // this is a comment. /* so is this, but the following is a statement: */ System.out.println(“Hello World“); } } • Java is case sensitive • public is an access modifier • Controls level of access other part of program have to this code • Everything in Java is a class – used to create building blocks • System.out is an object, calling its println method with parameter “Hello World”

18. Class • Class is a container for the program logic that defines the behavior of an application • Building blocks with which all Java applications and applets are built. • Everything in a Java program must be inside a class. • Following the keyword class is the name of the class. • Names must begin with a letter, and after that, they can have any combination of letters and digits.

19. Simple Template with Javadoc /** * This is a simple template, documented. * @version 0.01 * @author Your Name */ public classClassName{ public static voidmain(String[] args){ program statements; } }

20. The 8 Primitive Data Types in Java

21. Variables • For any meaningful program you need to modify data • Variables are used to store values • Operators operate on one or two variables • Forming expressions • Declare a variable called Name of type type: • type Name; • Example: • String name; int a, b; • Assigning Name a value val: • type Name=val; • Example: • String name=“Don Knuth”; int a=3; float k=3.3;

22. Integer Types • Range depends on size of each type: • long (8 bytes) -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 • int (4 bytes) -2,147,483,648 to 2,147,483,647 • short (2 bytes) -32,768 to 32,767 • byte (1 byte) -128 to 127 • All integer types are signed (the unsigned keyword does not exist in Java) • All integer types are the same size regardless of the device’s architecture

23. Representing Floating Point • Used for positive and negative numbers with fractional parts • Range and precision both depend on type • float (4 bytes) ±3.40282347*1038 • double (8 bytes) ±1.79769313486231570*10308 • Float stores up to 7 fractional digits • Double stores 15 decimal digits • In general, doubles should be used instead of Float • If speed or memory are constrained, floats may be necessary

24. Representing Characters • Unlike C, where char is almost always a single byte, a Java char can hold a multi-byte Unicode character • Every char is 16 bits (2 bytes), and stores either a complete character of Unicode U+0000 to U+FFFF or half of a U+10000 to U+10FFFF character • In most cases, String variable should be used to avoid having to worry about character types and lengths. • String pi = "\u03C0”; //π

25. Boolean Types • Can only indicate two values , true or false • Unlike C/C++, integer 0 and 1 are not equivalent to false and true • Avoid easy-to-create bugs. For example: if((x=1)) { statement; } //this would not compile in Java • Must use true and false when assigningboolean variables • No implicit conversion is possible betweenboolean and other data types

26. Strings • Java does NOT have a built-in string type • Standard library contains class called String • Every quoted string is an instance of this class • Java strings are sequence of Unicode characters • Example: “Java\u2122” consists of: J,a,v,a,™ • Example: String e = “”; //an empty string • String planet = “Earth”; • More later with String API

27. Enumerated Types • Sometimes variable should only hold a value • from specific (restricted) set • Example: • Shirt size allowed to be small, medium, large • You can, of course do: • int SMALL=1; • int MEDIUM=2; • int LARGE=3; • int shirtSize=one-of-the-above; • But nothing prevents one from setting shirtSize=-1; • Solution: enum’s: • Enum Size {SMALL, MEDIUM, LARGE}; • Size shirtSize=Size.one-of-the-above;