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

Contact Info Tavaris J. Thomas – – Google Group –

Any Programming Experience?

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 (8 th edition) – Cay S. Horstmann and Gary Cornel – ISBN:

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

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

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)

Java’s Evolution Java 1.0 First release Java 1.1 Inner classes Java (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

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

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

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

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!

Grabbing Java and Eclipse 1.Go to wnloads/index.html wnloads/index.html 2.Download Java SE 6 Update 37 JDK (includes the JRE) 3.Install the JDK 4.Install the JRE 5.Download Eclipse from: java-developers/heliossr2 6.Continue with installing Eclipse IDE

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“); }

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); }

“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”

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.

Simple Template with Javadoc /** * This is a simple template, documented Your Name */ public class ClassName{ public static void main(String[] args){ program statements; }

The 8 Primitive Data Types in Java

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;

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

Representing Floating Point Used for positive and negative numbers with fractional parts – Range and precision both depend on type – float (4 bytes) ± *1038 – double (8 bytes) ± *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

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 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

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 assigning boolean variables No implicit conversion is possible between boolean and other data types

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

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;