What is constructor

Having more than one occurrence of a constructor method in a class will throw a SyntaxError error. This code snippet is taken from the classes sample live demo. Here the prototype of Square class is changed—but the constructor of its base class Polygon is still called when a new instance of a square is created.

Leaving this out will cause a ReferenceError. A constructor initializes an object when it is created. It has the same name as its class and is syntactically similar to a method.

However, constructors have no explicit return type. A constructor is a special method of a class or structure in object-oriented programming that initializes an object of that type. A constructor is an instance method that usually has the same name as the class, and can be used to set the values of the members of an object, either to default or to user- defined values.

In class-based object-oriented programming, a constructor abbreviation: ctor is a special type of subroutine called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables. Constructor Definition Syntax. A class often has several constructors with different parameters. Each one builds the same class of object, but the different constructors use different sources of data for object initialization.

Usually the method that invokes a constructor saves the returned reference in a variable. Why are constructors used? The purpose of constructor is to initialize the object of a class while the purpose of a method is to perform a task by executing java code.

Constructors cannot be abstract, final, static and synchronised while methods can be. How many constructors can a class have? You can have constructors in a class According to Oracle docs. You can create many constructors but with different signatures. What is parameterized constructor? A constructor having a specific number of parameters arguments is called a parameterized constructor.

The parameterized constructor is used to provide different values to the objects, you can also provide the same values. Report Error. Your message has been sent to W3Schools. W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content.