Java Basic PART 1

why should you learn java

Java is easy to learn 

java is object oriented

java has rich API

powerful developement tools

GREAT COLLECTION OF OPEN SOURCE LIBRARIES

Wonderful community support

Java is FREE

Excellent documentation support - Javadocs

Java is Platform Independent

write once run anywhere

Java is Everywhere

Desktop, mobile,  card, and so Java programmers,
 organizations

Introduction 

Developed By : James Gosling 

Owner : Sun Microsystems 

Released in : 1995 

Stable Release : Java Standard Edition 7 (1.7.0) 

 OS : Cross Platform (Multi Platform)

 Extensions : .java, .class, .jar

JAVA Platform

 JAVA Platform It is Platform Independent. It compiles Java language code in Java bytecode , not in Machine code. A major benefit of using bytecode is porting.

Virtual machine 

ByteCode

Automatic Memory Management

JAVA Syntax

Commenting Methods

// /*  *//***@author yuri...*/ 

A Simple JAVA Program

class Hello {
    public static void main(String args []) 
       {
     System.out.println (“Hello"+                               "World”);        } 
}

Some abbreviations

 JDK : JAVA Development Kit

 JVM : JAVA Virtual Machine 

JRE : JAVA Runtime Environment 

javac : JAVA Compiler

 JVM : JAVA Virtual Machine 

 KVM : Kilobyte Virtual Machine 

CVM : Card Virtual Machine 

DVM : Delwik Virtual Machine 

Points to be remembered

Java programs need to be compiled only once.

 When a class is defined as public, class name and file name must be same. 

”;” can be put anywhere before a new statement. 

Java does not support operator overloading.

 Operator “+” is by default overloaded in JAVA.

Class

Template,

State and behaviour of object at run time, Abstract class ,Final class

Interface

 A 100% abstract class,

A contact for what a implementing class can do.

Behavioural purposes

Class can implement multiple interfaces

Variables

Primitives, Reference, Local variables Arrays, Final variables ,Transient

Methods

static

abstract

final

Encapsulation

 Keep data protected

Keep services open

Setters and getters method

Inheritance

 Re-usability

Sometimes we have no implementation

Is-a vs has-a relationship

Polymorphism

 Overloading

Overridding

Constructors

 Need?

Default constructor

Constructor overloading

Constructor calls in inheritance tree

operators

postfix     expr++ expr--
unary     ++expr --expr +expr -expr ~ !
multiplicative     * / %
additive     + -

equality     == !=

relational     < > <= >= instanceof

More operators

shift     << >> >>>
bitwise AND     &
bitwise exclusive OR     ^
bitwise inclusive OR     |
logical AND     &&
logical OR     ||
ternary     ? :
assignment     = += -= *= /= %= &= ^= |= <<= >>= >>>=

.equals() 

VS

==

exemple

 
 String user1 = "YuriLz";
 String user2 = "YuriLz";
 String user3 = "Yuritta";
 String user4 = new
               String("YuriLz");

 String user5 = new String();
 String user6 = new String();
   
 

 user5 = "YuriLz";
user6 += "YuriLz";

OUTSTREAM

 System.out.println( (user1==user2)? "Equal" : "Not Equal" );
 System.out.println( (user3==user2)? "Equal" : "Not Equal" );
 System.out.println( (user1==user2)? "Equal" : "Not Equal" );
 System.out.println( (user4==user2)? "Equal" : "Not Equal" );
 System.out.println( (user5==user2)? "Equal" : "Not Equal" );
 System.out.println( (user5==user6)? "Equal" : "Not Equal" );
 System.out.println( (user5.equals(user2))? "Equal" : "Not Equal" );
 System.out.println( (user5.equals(user3))? "Equal" : "Not Equal" );

(user1==user2)? "Equal" : "Not Equal" );
(user3==user2)? "Equal" : "Not Equal" );
(user4==user2)? "Equal" : "Not Equal" );
(user5==user2)? "Equal" : "Not Equal" );
(user5==user6)? "Equal" : "Not Equal" );
(user5.equals(user2))? "Equal" 
                     : "Not Equal" );
(user5.equals(user3))? "Equal" 
                     : "Not Equal" );

OUPUT

~$ javac StringsExemple.java~$ java StringsExemple
Equal
Not Equal
Not Equal
Equal
Not Equal
Equal
Not Equal 

THANKS!