Java Constructor

Constructor is defined in the class.
Constructor is similar to a method in the class.
Constructor name is same as class name.
Constructor does not have return data type.
Constructor can receive arguments.
Constructor is used to create and initialize the object.
If no constructor is defined in the class, then java provides default constructor.

Example

class student {
      int rollno;
      String name;
	  
      student() // constructor is defined, it has same name as class name 
      {
         rollno = 10;
         name = "Rajesh";
     }

      display ()
     {
       System.out.println ("roll no is " + rollno);
	   System.out.println ("name is "+ name);
	 }
}

class demostudent {
   public static void main (String args[])
	{

      student s1 = new student(); // this statement will call the constructor to 
					  // initialize s1 object.
         s1.diaplay();
      }
}

Explanation of the program

The program defines a class named 'student'.
Within the class 'student', a constructor is defined, it has same name as class name.
The constructor 'student' assigns values to variables.
The class 'demostudent' is defined to create and access class 'student'.
The statement 'student s1 = new student()' creates an object named s1.
The above statement is also initialize variables of the object s1 using constructor student().
The method display() is called using the object s1 to display values of variables.

Output of the program

roll no is 10
name is Rakesh

Parameterized Constructor

When we passing the arguments to constructor. It is called parameterized constructor.
Parametrized constructors are used to initialize the variables from user.

Example

class student {
      int rollno;
      String name;

      student(int r, String n) // Parametrized constructor 
      {
         rollno = r;
         name = n;
       }
      display ()
       {
           System.out.println ("roll no is " + rollno);
	       System.out.println ("name is "+ name);
	    }
}


class demostudent {
   public static void main (String args[])
	{
      student s1 = new student(10, "Rajesh"); // this statement will call the constructor to 
						// initialize s1 object.
         s1.diaplay();
      }
}

Explanation of the program

In the above program, two arguments are passed to constructor 'student'.
Arguments are assigned to variables of the object s1.

Output of the program

roll no is 10
name is Rakesh

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