Important concepts in JAVA

Class:
Class is an entity that represents the state or behaviour of the object.Class may contain data members and member functions.
Syntax:
Class First
{
          public static void main(String[]  args)
          {
                 System.out.println("Fun to learn JAVA");
          }
}

public static void main(String[] args)

public :- The method main() can be accessed by anything including interpreter.

Static :- This keyword tells the compiler that the main() method is used in the class. There is no need of instance to execute the static method.

Void :- it indicates that the main function should not return any value.

String args[] :- the main method is declare with a single parameter “args” which is a type of String array.

COMPILING AND RUNNING THE JAVA PROGRAM

Step1: Type the program in a notepad and save as classname.java and place it in the C:\Program Files\Java\jdk1.7.0_17\bin

Step 2 : open the command prompt change the path to C:\Program Files\Java\jdk1.7.0_17\bin and then to compile type javac classname.java, to run type java classname

Step 3 : output will be displayed.

Instead running the program in command prompt better we can use IDE like netbeans or eclipse.

VARIABLES & SCOPE

There are two ways to describe variables:

à   Variable of primitive type

à   Variable of reference type

We can declare variable inside a method or outside a method.

Variable which is defined inside a method is called local variable. Sometime this is also called as automatic, temporary or stacks variables.

Variable defined outside a method are created when the object is constructed using the new abc() call. Variable can be define outside a method in two ways,

à   Using static keyword is called class variable.

à   Without using static keyword is called as instance variable or member variable.

DEFAULT VALUE OF PRIMITIVE TYPES

VARIABLE	VALUE
Byte	0
Short	0
Int	0L
Long	0.0F
Float	0.0D
Double	‘\u0000’
Boolean	False
All reference types	null

OPERATORS

Important types of operators are there in java programming language.

à   Arithmetic Operator (+, -, *, /)

à   Logical Operator (AND (&), OR (|), NOT (!), XOR (^))

à   Short-circuit logical Operator (&&, ||)