difference between static and instance variable with code examples

In object-oriented programming, variables play a vital role in storing and manipulating data. There are two types of variables in Java programming; static and instance variables. Both these variables are used to store and manage data, but they differ in the way they are declared, accessed, and utilized.

Static Variables
A static variable refers to a variable that is declared with the keyword "static". Unlike instance variables, a static variable is shared across all the objects of a class. In other words, there is only one copy of the static variable that is shared among all instances of the class. Static variables are defined in the class level, which means the variable can be accessed without instantiating the class. Static variables are also known as class variables as they are associated with the class rather than the object of a class.

Here is an example code snippet to showcase static variables.

public class Employee {
static String department = "Engineering";
String name;

  public static void main(String args[]) {
     Employee emp1 = new Employee();
     Employee emp2 = new Employee();

     emp1.department = "Management";
     emp2.department = "Sales";

     System.out.println(emp1.department);
     System.out.println(emp2.department);

}
}

Output:
Sales
Sales

In the above code, the department variable is declared as static. When the instances emp1 and emp2 are created, both refer to the same variable. Therefore, changing the value of the variable using one instance results in the change being reflected in all instances of that class.

Instance Variables
Instance variables are declared inside a class and outside of any method. Instance variables are specific to objects or instances of a class and are accessed by using the object reference. Each instance of the class has its copy of the instance variable, and their value may differ. Instance variables are used to represent the state of an object and are often initialized through the use of constructors.

Here is an example code snippet to showcase instance variables:

public class Animal {
String name;

  public static void main(String args[]) {
     Animal animal1 = new Animal();
     Animal animal2 = new Animal();

     animal1.name = "Lion";
     animal2.name = "Tiger";

     System.out.println(animal1.name);
     System.out.println(animal2.name);

}
}

Output:
Lion
Tiger

In the above code, we have an instance variable "name" inside the Animal class. The "name" variable can have different values for each object as we assign different values to it while creating object "animal1" and "animal2" and accessing it using their respective object references.

Differences between Static and Instance Variables

1. Declaration: The Static variable is declared using the static keyword, while the instance variable is declared without using any keyword except access modifiers.
2. Memory Allocation: A single copy of the static variable is created, whereas for every object, a new copy of an instance variable is created.
3. Storage: Static variables are associated with the class and are stored separately from the object. At the same time, instance variables are associated with the object and are stored within the object memory.
4. Value Access: Static variables can be accessed using the class name, but instance variables can only be accessed by creating an object of a class.
5. Scope: The scope of the static variable is global, which means it can be accessed from any method or instance of that class, whereas the instance variable's scope is local, which means it can be accessed from within that particular method.

Conclusion
In conclusion, both static and instance variables play an essential role in Java programming. While both these variables store and manage data, they differ in the way they are declared, accessed, and utilized. Static variables are used when there is a need to store or modify the data that is common across all instances of a class. Instance variables are used when it is needed to store or modify data that is unique to each object or instance of a class. Understanding the differences between static and instance variables is crucial to utilize them effectively in Java programming and develop efficient and robust applications.

1. Inheritance in Object-Oriented Programming
   Inheritance is one of the fundamental concepts of object-oriented programming, and it allows objects of one class to be used in place of objects of another class. This concept provides code reusability, maintainability, and extensibility. Inheritance is implemented by creating a new class derived from an existing class called the base class or super class. The new class is called the derived class or sub class. The derived class inherits all the properties and methods of the base class and can also add its own unique properties and methods.

Here is an example code snippet to showcase inheritance in Java:

public class Shape {
protected String color;

public Shape(String color) {
this.color = color;
}

public void draw() {
System.out.println("Drawing a shape.");
}
}

public class Circle extends Shape {
private int radius;

public Circle(String color, int radius) {
super(color);
this.radius = radius;
}

public void draw() {
System.out.println("Drawing a circle with color " + color + " and radius " + radius);
}
}

Output:
Drawing a circle with color Blue and radius 5

In the above code, the Circle class extends the Shape class, and it inherits the "color" variable and "draw()" method from the Shape class. The Circle class also adds its own unique property "radius" and redefines the "draw()" method to print a Circle's specific details.

2. Abstraction in Object-Oriented Programming
   Abstraction is the process of hiding complex implementation details and providing a simplified interface to the end-users. Abstraction enables us to work at a higher level of abstraction without worrying about low-level details that are not relevant to the current task. It can be implemented using abstract classes and interfaces. An abstract class is a class that cannot be instantiated, but it can be extended. Abstract classes contain one or more abstract methods, which are methods without implementation. The implementation of abstract methods is provided by the subclasses. An interface is a collection of abstract methods, and it also provides a way to achieve abstraction in Java.

Here is an example code snippet to showcase abstraction in Java:

public abstract class Vehicle {
protected String make;

public Vehicle(String make) {
this.make = make;
}

public abstract void start();
}

public class Car extends Vehicle {
public Car(String make) {
super(make);
}

public void start() {
System.out.println("Starting a " + make + " car.");
}
}

Output:
Starting a BMW car.

In the above code, the Vehicle class is an abstract class with an abstract method start(). The Car class extends the Vehicle class and implements the start() method. The start() method's implementation is provided by the Car class, and the make variable's value is provided by the super class, Vehicle. The start() method's implementation can vary depending on the type of vehicle, but the make variable always comes from the Vehicle class as it is a common property of all vehicles.

In conclusion, inheritance and abstraction are two essential concepts of object-oriented programming that enable us to build complex yet maintainable and scalable applications. Understanding these concepts is crucial for any Java developer to write high-quality code that is easy to maintain and extend.

Popular questions

1. What is a static variable?
   A static variable is a type of variable in Java that is declared with the keyword 'static'. It is associated with the class rather than the object of a class and is shared across all instances of a class.

2. What is an instance variable?
   An instance variable is a type of variable in Java that is declared inside a class and outside of any method. It is specific to objects or instances of a class and is accessed by using the object reference.

3. How are static variables and instance variables different in terms of memory allocation?
   A single copy of the static variable is created, whereas for every object, a new copy of an instance variable is created.

4. How can you access static variables and instance variables?
   Static variables can be accessed using the class name, while instance variables can only be accessed by creating an object of a class.

5. What is the scope of a static variable and an instance variable?
   The scope of the static variable is global, which means it can be accessed from any method or instance of that class. At the same time, the instance variable's scope is local, which means it can be accessed from within that particular method.

Tag

"Variable-Types"