A constructor is similar to method and it is invoked at the time creating an object of the class, it is generally used to initialize the instance variables of a class. The constructors have same name as their class and, have no return type.
There are two types of constructors parameterized constructors and no-arg constructors the main purpose of a constructor is to initialize the instance variables of a class.
Example
In the following example we are trying to initialize the instance variables of a class using no-arg constructor.
public class Test { int num; String data; Test(){ num = 100; data = "sample"; } public static void main(String args[]){ Test obj = new Test(); System.out.println(obj.num); System.out.println(obj.data); } }
Output
100 sample
Example
In the following example we are trying to initialize the instance variables of a class using parameterized constructor.
import java.util.Scanner; public class Test { int num; String data; Test(int num, String data){ this.num = num; this.data = data; } public static void main(String args[]){ Scanner sc = new Scanner(System.in); System.out.println("Enter a string value: "); String data = sc.nextLine(); System.out.println("Enter an integer value: "); int num = sc.nextInt(); Test obj = new Test(num, data); System.out.println(obj.num); System.out.println(obj.data); } }
Output
Enter a string value: sample Enter an integer value: 1023 1023 sample