Variables in Java Explained: Local, Static, and Instance

Variables in Java

A variable is a symbolic name associated with a value. The value of a variable can change during program execution.

In Java, variables are classified into three types:

1. Local Variable
2. Static Variable
3. Instance Variable

1. Local Variable

A local variable is declared inside a method, constructor, or block.

Key points:

• Also called a method-level variable
• Accessible only within the block {} where it is declared
• Does not support default values
• Must be initialized before use
• If declared but not initialized and used, it causes a compile-time error
• If declared but not used, no error is generated

Example:

void display() {

    int x = 10; // local variable

    System.out.println(x);

}

2. Static Variable

A static variable is declared inside a class but outside any method, using the static keyword.

Key points:

• Also called a class-level variable
• Supports default values
• Memory is allocated once and shared among all objects

• Can be accessed:

    By variable name (within the same class)
    By ClassName.variableName (from another class)

Example:

class Example {

    static int count = 5;

}

3. Instance Variable

An instance variable is declared inside a class but outside any method, without using the static keyword.

Key points:

Also called an object-level variable

Supports default values

Each object gets its own copy

Accessed using object creation

Example:

class Student {

    int id; // instance variable

}

Variable Declaration and Initialization
Syntax:

dataType variableName = value;

Example:

int number = 10;

Initialization

Initialization is the process of assigning a value to a variable for the first time.

Reinitialization

Reinitialization is the process of assigning a new value to an already initialized variable.

The previous value is replaced

The new value is stored in the variable

Example:

int x = 5;

x = 10; // reinitialization