What is a constructor? How It is different from other methods?
What is a constructor:
A constructor is a special method defined in a class implicitly or explicitly. Its purpose is to initialize the instance variables of a class.
How It is different from other methods?
Differences between Constructor and other class methods:
A constructor is different from the other class methods in three ways.
- A constructor is always a public method, while other might be public, private or protected.
- A constructor returns nothing even it does not use ‘void’ keyword in its definition. While others might have return something.
- Constructor has the same name as that of the class
Example:
Consider a class student:
public class Student { // instance variables private int rollNo ; private String stdName ; // a constrcutor public Student(int aRollNo, String aName) { rollNo = aRollNo ; stdName = aName ; } // rest-of-the-class-members } // End-class-Student
How a constructor is called:
Consider a demo class / test class StudentDemo
public class StudentDemo { public static void main(String[] args) { // creating an object std of above class Student // it will create a new student with rollno = 2501 and // stName = "Muhammad Rizwan" Student std = new Student(2501, "Muhammad Rizwan") ; // rest of the logic } } //end-class-studentdemo