Constructors

Need Of Constructor

class Student {
String name;
int rollno;


/* constructor */
Student(String name , int rollno){
this.name = name;
this.rollno = rollno;
}

public static void main(String[] args){
Student s = new Student();
Student s1 = new Student();

}
}

• So if we create objects , a separate copy will be created.
• Constructor is used to initialize an object

• ClassName objname =new Constructor();

  Student s = new Student ("Vamsi" ,1);

Rules

• Constructor name should be equal to class name.
• It doesn't have any return type. because you are not calling the constructor , if you are calling you can expect something, here JVM will execute automatically.
• Access modifiers supported are public,default,protected,private.

Types of Constructors:

Default constructor

  class Test{
  //Default constructor
  }

• If you don't add constructor in the class , compiler will add it.
• Every class in java, including abstract class will have constructor.
• If you are writing atleast one constructor, compiler will not generate default constructor.

prototype of default constructor: 1. It is always no-arg constructor 2. Access modifiers applicable - public , default. 3. It is a no-arg to super class constructor.

No-Arg constructor

 class Student {
 String name;
 int rollno;

/* constructor */
Student(){

}

Parameterized constructor

  class Student {
  String name;
  int rollno;

/* constructor */
Student(String name , int rollno){
this.name = name;
this.rollno = rollno;
}
}