Java Basics Help

Data Types:
 
There are two data types available in Java:

• Primitive Data Types
  There are eight primitive data types supported by Java. Primitive data types are predefined by the language and named by a keyword.
  
  byte,short,int,long,char,double,float,boolean
  
• Reference/Object Data Types
  
  • Reference variables are created using defined constructors of the classes. They are used to access objects. These variables are declared to be of a specific type that cannot be changed. For example, Employee, Puppy etc.
  • Class objects, and various type of array variables come under reference data type.
  • Default value of any reference variable is null.
  • A reference variable can be used to refer to any object of the declared type or any compatible type.

Variables:

You must declare all variables before they can be used.
The basic form of a variable declaration is shown here:

data type variable [ = value][, variable [= value] ...] ;

Here data type is one of Java's datatypes and variable is the name of the variable. To declare more than one variable of the specified type, you can use a comma-separated list.

Following are valid examples of variable declaration and initialization in Java:

int a, b, c;         // Declares three ints, a, b, and c.
int a = 10, b = 10;  // Example of initialization
byte B = 22;         // initializes a byte type variable B.
double pi = 3.14159; // declares and assigns a value of PI.
char a = 'a';        // the char variable a iis initialized with value 'a' 

There are three kinds of variables in Java:

• Local variables
• Instance variables
• Class/static variables

Local Variable

A variable that is declared inside the method is called local variable.

Instance Variable

A variable that is declared inside the class but outside the method is called instance variable . It is not declared as static.

Static variable

A variable that is declared as static is called static variable. It cannot be local.