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Tutorials > Java > Java classes objects inheritance and polymorphism Guide

Java Classes, Objects, Inheritance & Polymorphism Guide

Understanding object-oriented programming (OOP) in Java is key to building scalable and maintainable applications. This tutorial introduces you to four fundamental OOP concepts: classes, objects, inheritance, and polymorphism. A class acts as a blueprint, while objects are instances that bring the blueprint to life. Inheritance enables code reuse by allowing one class to inherit properties and behaviors from another. Polymorphism allows different classes to respond differently to the same method call. With real-world examples and simple syntax, this guide makes it easy to grasp core OOP principles in Java.

Java classes are the building blocks of object-oriented programming in Java. A class is a blueprint that defines the properties and methods of an object. For example:
class Dog {
   String breed;
   int age;

   public void bark() {
      System.out.println("Bark!");
   }
}

In this example, the Dog class has two properties (breed and age) and one method (bark).

Objects are instances of classes. You can create an object from a class by using the new operator. For example:

Dog myDog = new Dog();
myDog.breed = "Labrador";
myDog.age = 5;
myDog.bark();

In this example, a Dog object named myDog is created and its properties are set. The bark method is also called on the myDog object.

Inheritance is a mechanism that allows you to create a new class based on an existing class. The new class inherits all the properties and methods of the existing class and can also have its own unique properties and methods. For example:

class Labrador extends Dog {
   public void fetch() {
      System.out.println("Fetch!");
   }
}

In this example, the Labrador class is created as a subclass of the Dog class. The Labrador class inherits all the properties and methods of the Dog class and adds its own unique method, fetch.

Polymorphism is a mechanism that allows objects of different classes to be treated as objects of a common class. Polymorphism is achieved through method overriding, which is the ability of a subclass to provide a new implementation of a method defined in its superclass. For example:

class Animal {
   public void makeSound() {
      System.out.println("Animal sound");
   }
}

class Cat extends Animal {
   @Override
   public void makeSound() {
      System.out.println("Meow");
   }
}

Animal myAnimal = new Cat();
myAnimal.makeSound();
In this example, the Cat class overrides the makeSound method of its superclass, Animal. When the makeSound method is called on a Cat object, the override version of the method is executed. This demonstrates polymorphism, as the object of the Cat class can be treated as an object of the Animal class.

Mastering classes, objects, inheritance, and polymorphism is essential for writing robust, object-oriented Java applications. These principles form the backbone of Java development, enabling code reuse, modularity, and flexibility. Keep practicing by building small programs that use class hierarchies and overridden methods to reinforce your learning. Continue exploring more advanced Java OOP concepts on itcodescanner.com to grow your development skills.

FAQ Section

Q1. What is the difference between a class and an object in Java?
A class is a blueprint, while an object is an instance of that class created at runtime.

Q2. What does the extends keyword do in Java?
It allows a subclass to inherit from a superclass, gaining its properties and methods.

Q3. What is method overriding in Java?
Overriding means redefining a method from the superclass in the subclass with the same signature.

Q4. How is polymorphism implemented in Java?
Polymorphism is achieved through method overriding and dynamic method dispatch at runtime.

Q5. Can a class inherit from multiple classes in Java?
No, Java does not support multiple inheritance with classes. It can be done using interfaces.



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