What is constructor in OOP?

 Object-oriented programming (OOP) is a programming paradigm in which computer programs are built from abstractions of data or objects that have features and behavior. In OOP, the programmer designs the program by creating objects— also called instances of an object class — and then creating functions to operate on these objects.

An object’s features are what the user can see. An initialization function for an object is called a function Object() { [native code] }. For example, in the Car class shown below, the constructor is used to initialize a Car object with values for weight and speed.

read also : How are getters and setters implemented in Java?

 What is constructor in OOP?

 An initialization function for an object is called a function Object() { [native code] }. It’s a special method defined in an object’s class that initializes new instances of that class. Some OOP languages, such as C#, Java, and C++, allow programmers to contain code within constructors so they can perform initialization tasks immediately without instantiating an object first. The instance doesn’t exist yet when the constructor runs. This makes it possible to perform initialization tasks in one place instead of repeating them throughout the code. Doing so saves development time by eliminating repetition. 

Constructors are called automatically when objects are created: new expressions instantiate objects and call their constructors. In Java, newInstance() calls a constructor for every newInstance() call:

new Car("Mercedes","Benz").make(); // Mercedes makes for this car

This is because there’s no way to tell when calling newCar() whether it will create one instance for Mercedes or many for all other cars as well— hence the need for a single instance per creation call to avoid this potential problem. Using a single instance per call ensures that all instances will have the same state at creation time regardless of how many times they’re instantiated later using new expressions. 

Declaring a constructor early in the object’s definition can make your code clearer; it tells readers what will happen if they instantiate your class before defining its methods and attributes later. In this example from Ruby on Rails, if you instantiate Vehicles before defining methods such as create vehicle(), you get an error message:

class Vehicle < ActiveRecord::Base def self . createVehicle @vehicle ||= Vehicle . create( @vehicle_id ) end end

 Although constructors appear complex at first glance since they initialize newly created objects, declaring them early can make your code easier to understand since it informs readers what will happen when they instantiate your classes instead of leaving them guessing until later code definitions define what happens with each instance creation call.