Java Variable

A variable in Java is a named memory location used to store data that can change during program execution.

Variable = name + memory + value

Why use variables

• Store data temporarily in memory
• Reuse values multiple times
• Perform calculations
• Make programs dynamic and flexible
• Improve code readability and maintenance

How is a variable created in Java

variable is created in two steps:

1.Declaration (Memory allocation)

- int age;
- Tells Java what type of data to store
- Reserves memory

2.Initialization (Assign value)

  Stores the value in allocated memory
  int age = 25

When is a variable created?
It depends on the type of variable
Java has 4 main types of variables based on where and when
memory is allocated.

1. Local Variable

** Where created?**
Inside a method, constructor, or block

When created?
When the method is called

When destroyed?
When the method execution ends

Memory location: Stack

void show() {
    int x = 10; // local variable
}

• Must be initialized before use
• No default value

2.Instance Variable (Non-static)

Where created?
Inside class but outside methods

When created?
When an object is created using new

** When destroyed?**
When object is destroyed (GC)

Memory location: Heap

class Student {
    int id; // instance variable
}

Student s = new Student(); // instance variable created here

Gets default value
One copy per object

3.Static Variable (Class Variable)

Where created?
Inside class with static keyword

** When created?**
When class is loaded into JVM

When destroyed?
When class is unloaded

Memory location: Method Area (Class Area)

class College {
    static String collegeName = "ABC College";
}

Single copy shared by all objects
Access using class name

4.Parameter Variable

Where created?
In method parameter list

When created?
When method is called

Memory location: Stack

void add(int a, int b) {
    int sum = a + b;
}