Java – Class Members

Class Members:

• The Members which we can define inside the class.
• Class Members includes
  • Variables
  • Methods
  • Blocks
  • Constructor

Variables: Variable stores information of class(object).We store information in java using 4 types of variables

• Static Variables:
  • A variable with static keyword inside class and outside to methods.
  • Static variables store common information of all Objects.
  • Static variables get memory only once.
  • Static variables can access using class-name.
• Instance Variables:
  • A variable inside class and outside to methods.
  • Instance variables store specific information of all Objects.
  • Instance variables get separate memory for each object.
  • Instance variables can access using Object-Reference.
• Method Parameters:
  • A variable inside the method definition parenthesis.
  • Parameters are used to store input in a Method.
  • Parameters can access directly but only inside that method.
• Local Variables:
  • A variable inside the method body.
  • Store processed information inside the Method.
  • Access local variables directly and only inside the method.

Blocks:

• Block is a set of instructions without identity
• Block is either static or instance(anonymous)

Static Block: Defining a block using static-keyword. JVM invokes static block when class execution starts.

static {             statements; }

Instance Block: Defining a block without static-keyword. JVM invokes instance block every time when object creates.

{             statements; }

Methods:

• A Block of instructions with an identity.
• Method takes input, process input and returns output
• Methods performs operations on data

Static Method: Defining a method using static keyword. We can access static methods using class-name.

static void display() {             logic; }

Instance Method: Defining a method without static keyword. We can access instance methods using object-reference.

void display() {             logic; }

Constructor: Defining a method with class name. Return type is not allowed. We must invoke the constructor in object creation process.

class Account {             Account(){                         statements;             } }