09. variables and Literals.md

09. variables and Literals

Variables

• It is a named memory location that holds the data value of a particular data type.

  Declaration: 
  	dataType variableName; 
  
  Initialization: 
      dataType variableName = value; 
              **OR**
      dataType variableName; 
      variableName = value; 
  

Variable Naming rules:

• cannot contain white spaces
• can begin with a special character dollar ($) and underscore ( _ )
• first letter of a variable cannot be a digit
• camelCase convention should be used
• Built in keywords ( int, for, while, class, break, continue, etc ) cannot be used

Types of variables:

• Local:
  • declared within a body of method, constructor or code block.
  • scope is limited within that block.
  • created within the method or block and destroyed after the method invocation.
  • No initialization ( no default values ), if not initialized compile time error
  • stored in stack
• Instance
  • declared inside the class but outside any method, constructor or block body
  • not shared between objects.
  • scope is tied to the instance or object of the class.
  • created with the new keyword and destroyed when the object is destroyed.
  • default values are given if not initialized
  • stored in heap
• Static ( Class Variable )
  • declared inside a class but not inside the method, constructor or a block, with the static keyword
  • shared with all instances of class.
  • scope is tied to the class itself.
  • created at the start of the program and destroyed at the end of the program.
  • default values are given if not initialized
  • stored in Method Area or Class Area

Literals

• The data items that have fixed or constant values.

int number = 20;
//int -> data type
//number -> variable 
//20 -> literal

Types:

1. Integer literals

2. Floating literals

3. Boolean literals

4. Character literals

5. String literals

6. Null literal