What are instance variables?

Instance variables are variables belonging to a specific instance (object) of a class. Each object has its own copy of these variables.

• Defined inside the class but outside of methods.
• Accessible from any method of the same class.
• Their value is unique for each instance of the object.
• Initialized when the class instance is created (for example, in the constructor).

Example in Java:

public class Dog {
    String name; // instance variable

    public Dog(String name) {
        this.name = name;
    }

    public void printName() {
        System.out.println("My name is " + this.name);
    }
}

// Creating instances
Dog dog1 = new Dog("Buddy");
Dog dog2 = new Dog("Lucy");

// Each instance has its own 'name'
dog1.printName(); // Output: My name is Buddy
dog2.printName(); // Output: My name is Lucy

Comparison table:

Variable	Belongs to	Scope	Lifecycle	Initialization
Instance variable	Each object instance	Inside the instance	As long as the instance exists	When the instance is created (constructor)
Static (class) variable	Belongs to the class itself (shared by all)	Everywhere in the class (often public)	Until the program ends	When the class is loaded
Local variable	Specific method or code block	Inside the method/block where declared	Only during the execution of the method/block	Must be initialized before use