? Variable Scope & Lifetime in Java

? Quick Overview

In Java, scope defines where a variable can be accessed, while lifetime defines how long the variable exists in memory. Understanding both is essential for writing clean, efficient, and bug-free programs.

? Key Concepts

• Scope controls visibility of variables
• Lifetime controls existence in memory
• Java has local, instance, and static variables
• Memory allocation depends on variable type

? Syntax & Theory

• Local Variables → Declared inside methods or blocks (Stack Memory)
• Instance Variables → Declared inside class, outside methods (Heap Memory)
• Static Variables → Declared with static keyword (Static/Metaspace Memory)

? Code Examples

// Demonstrating variable scope and lifetime
class ScopeDemo {
  
  // 1. Static Variable (Class Scope)
  static int staticVar = 20;

  // 2. Instance Variable (Object Scope)
  int instanceVar = 10;

  void showScope() {
    // 3. Local Variable (Method Scope)
    int localVar = 30;
    
    System.out.println(localVar);
    System.out.println(instanceVar);
    System.out.println(staticVar);
  }
}

? Live Output / Explanation