Introduction to Java programming

Tuesday, September 10, 2013 TOPS Technologies - Java Tutorial

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TOPS Technologies – Java Introductory Tutorial Module :1( theory) http://www.tops-int.com/

TOPS Technologies – Java Introductory Tutorial

INTRODUCTION TO JAVA

WELCOME • • • • • • • • • •

History First Java Application Data types Variables Strings Assignments Math, Boolean expressions Relational operations If statements System.exit

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VERY BRIEF HISTORY • •

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Started in 1991 by SUN Microsystems Targeted at consumer electronics. Wanted reliable programming language.

Integrated into browsers Evolved into write once run anywhere, integrates into Netscape General purpose libraries released

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COURSE INFORMATION 

Textbook: Java in a Nutshell Reading class 1 chapters 1,2

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BASIC DEFINITIONS •

Java is an object oriented language.

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Object Method Class Applications Applets Native classes Threads Exceptions

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FIRST APPLICATION /** *Hello World, first application, only output. */ import java.io.*; public class hello{ public static void main (String [] args) { System.out.println(“Hello World\n”); } //end main }//end class

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HOW TO GET IT RUNNING •

Text in hello.java file •

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To compile: •

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Why? javac hello.java

To run: •

java hello

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NOTICE: • • •

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Java is CASE SENSITIVE!!

Whitespace is ignored by compiler Whitespace makes things easier to read…hence it affects your grade  File name has to be the same as class name in file.

Need to import necessary class definitions

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VARIABLES •

Variables: • • •

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Name Type Value

Naming: • • • • •

May contain numbers,underscore,dollar sign, or letters Can not start with number Can be any length Reserved keywords Case sensitive

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PRIMITIVE DATA TYPES Byte Short Int Long Float Double Boolean Char

8 16 32 64 32 64 1 16

-27 -215 -231

27-1 215-1 231-1

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1

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ASSIGNMENT • • • • • •

= Example: int n; n = 10; or int n = 10; //same

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STRINGS • • • •

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Not a primitive class, its actually something called a wrapper class To find a built in class’s method use API documentation.

String is a group of char’s A character has single quotes • char c = ‘h’; A String has double quotes • String s = “Hello World”; Method length • int n = s.length;

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USING STRINGS public class hello{ public static void main (String [] args) { String s = “Hello World\n”; System.out.println(s); //output simple string } //end main }//end class hello

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MATH •

Unary •

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Regular math (+,-,*,/) •

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int x = -9; int y = 3+x;

% modulo operator

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INCREMENTING • • •

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Increment and Decrement i++ equivalent to i = i + 1; Can also do ++i, which uses i before incrementing it.

Decrementing: i--;

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CASTING int n = 40; Wrong : byte b = n; why??

Right: byte b = (byte) n; Type casting converts to target type

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CASTING II •

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Type char is stored as a number. The ASCII value of the character.

A declaration of : •

char c = ‘B’; stores the value 66 in location c can use its value by casting to int how??

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ASSIGNMENT • • • • •

+= -= *= /= %=

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BOOLEAN EXPRESSIONS •

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boolean b b will be either true (1) or false (0) Logical operations: !(not), && (and) || (or) boolean a,b; a = true; b = false; System.out.println (“a && b is “ + (a && b));

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RELATIONAL OPERATORS  ==  != > <  >=  <=

equality inequality greater than less than greater than or equal to less than or equal to

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THE IF - BRANCHING STATEMENT •

if ( x < y) { x = y; • } •

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if ( x < y ) { x = y; } else { x = 88; }

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IF/ELSE â&#x20AC;˘

if (logic condition) { something } else if (logic condition) { something } else { something else }

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NESTED IF if ( x < 0 ) { System.out.println( “ x is negative “ ); } else { if ( x > 0 ) { System.out.println ( “x is positive” ); } //end if x > 0 else { System.out.println ( “x is zero “ ); } } //end else x >=0 TOPS Technologies – Java Introductory tutorial M1

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SWITCH/CASE Switch(variable) { case(1): something; break; case(23): something; break; default: something; }

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EXCEPTIONS • •

Java exception object. java.io.Exception most general one.

Some exception like in Throwable class define methods to get the message.

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TRY….CATCH BLOCKS. Try { ……. } catch ( IOException v) { ………. }

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SYSTEM.OUT.PRINTLN • •

println is a method in the Printstream class.

Defined: •

public void println(String x) can be any type of string or combination string using addition to join parts.

Example: println(“hello “ + “world “ + x);

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SYSTEM.EXIT() • • • • •

One method in java.lang.System Defined: public static void exit ( int status) Terminates currently running Java VM Status is status code, non zero will usually mean something abnormal.

Used at end to indicate success, or in middle to signal problems.

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