Introduction to Java

Tavaris J. Thomas Ph.D.BNAI ZION SCIENTISTS DIVISION

JOB ORIENTATION & TERMINOLOGY CLASSES

Fall 2012

Contact Info

• Tavaris J. Thomas– tavaris@gmail.com– www.ee.cooper.edu/~tthomas/java

• Google Group– http://groups.google.com/group/bz-java

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 (8th edition)– Cay S. Horstmann and Gary Cornel– ISBN: 0132354764

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 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

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 http://www.oracle.com/technetwork/java/javase/downloads/index.html

2. Download Java SE 6 Update 37 JDK (includes the JRE)3. Install the JDK4. Install the JRE5. Download Eclipse from:

http://www.eclipse.org/downloads/packages/eclipse-ide-java-developers/heliossr2

6. Continue with installing Eclipse IDE

Hello World Example

• Simplest possible program: prints one line• Will re-visit this program laterpublic class HiWorld {

public static void main(String[] args) {

System.out.println(“Hello World“);

}

}

Another Example

• Uses an array of three strings and a looppublic 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 isa 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.

* @version 0.01

* @author 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) ±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

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

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;