Variables in Java

In Java, variables are containers that hold data, and they play a crucial role in programming by allowing us to "store", "manipulate", and "retrieve" values within a program.

Here's an explanation of Java variables:

Declaration:

Before using a variable, we need to declare it, specifying its name and type.

Syntax:

type variableName;

int age;

Initialization:

After declaring a variable, we can optionally initialize it with a value.

Initialization assigns an initial value to the variable.

Syntax:

type variableName = value;

int age = 15;

Types of Variables:

Primitive Variables:

Primitive variables hold simple data types directly.
These variables hold primitive data types such as integers, floating-point numbers, characters, booleans, etc. Examples include int, double, char, boolean, etc.

Example:

// Declaration and initialization of an integer variable
int age = 20;

or

int age; // Declaration
age = 20; // Initialization

// Declaration and initialization of a boolean variable
boolean isStudent = true;

Reference Variables:

Reference variables hold references (memory addresses) to objects.
These variables hold references (memory addresses) to objects. Examples include objects of classes, arrays, etc.
They are declared with the class name.

Example:

// Declaration and initialization of a String object reference

String name; // Declaration
name = "Alice"; // Initialization

Local Variables:

Local variables are declared within methods, constructors, or blocks.
They are accessible only within that scope.
local variables within a method:

Example:

void greet() {
    String msg = "Hi, This Message is from Local Variable!"; // Local Variable
   
   // msg is only accessible within this method
    System.out.println(msg);
}

Instance Variables:

Instance variables are associated with instances (objects) of the class.
Each instance of the class has its own copy of instance variables.
Instance variables within a class:

Example:

class Employee {
    String name; // Instance Variable
    int age; // Instance Variable
}

Lifetime:

Describes how long a variable exists in memory.

Local variables exist only within the method or block where they are declared. Instance and static variables exist as long as the object or class exists.

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