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. • • • • • • • •
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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