Constructors in Java

 Constructors in Java

  • In Java, a constructor is a block of codes similar to the method. 

  • It is called when an instance of the class is created. 

  • At the time of calling constructor, memory for the object is allocated in the memory.

  • It is a special type of method which is used to initialize the object.

  • Every time an object is created using the new() keyword, at least one constructor is called.

  • It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.
  • There are two types of constructors in Java: no-arg constructor, and parameterized constructor.
  • Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.

Rules for creating Java constructor:-

There are two rules defined for the constructor.

  1. Constructor name must be the same as its class name

  2. A Constructor must have no explicit return type

  3. A Java constructor cannot be abstract, static, final, and synchronized

Types of Java constructors:-
  1. no-arg constructor or Default constructor
  2. parameterized constructor.
Java Default  Constructor:-

A constructor is called "Default Constructor" when it doesn't have any parameter.

Syntax of default constructor:

<class_name>() Example:- Test()

 {Code}                                                {Cod}    

Example of default constructor:-

class Bike1

{    

Bike1()  

{

System.out.println("Bike is created");

}  

 public static void main(String args[]){   

Bike1 b=new Bike1();  

}  

}  

Java Parameterized Constructor:-

  • A constructor which has a specific number of parameters is called a parameterized constructor.

Syntax of Parameterized Constructor:-
<class_name>(Args)
{
code;
}

Ex:-
Test(int i , int j)
{
code ;
}
Example of Parameterized Constructor:-

class Student4{ 

    int id;  

    String name;  

    Student4(int i, String n){  

    id = i;  

    name = n;  

    }  

    

    void display(){System.out.println(id+" "+name);}  

   public static void main(String args[]){  

      Student4 s1 = new Student4(111,"om");  

    Student4 s2 = new Student4(222,"priya");  

    s1.display();  

    s2.display();  

   }  

}  

Constructor Overloading in Java:-

  • In Java, a constructor is just like a method but without return type. It can also be overloaded like Java methods.

  • Constructor overloading in Java is a technique of having more than one constructor with different parameter lists. 

  • They are arranged in a way that each constructor performs a different task. 

  • They are differentiated by the compiler by the number of parameters in the list and their types.


Example of Constructor Overloading in Java:-

class Student5{  

    int id;  

    String name;  

    int age;   

    Student5(int I, String n)

{  

    id = i;  

    name = n;  

    }  

     Student5(int I, String n, int a)

{  

    id = i;  

    name = n;  

    age=a;  

    }  

    void display(){System.out.println(id+" "+name+" "+age);}  

   

    public static void main(String args[]){  

    Student5 s1 = new Student5(111,"Karan");  

    Student5 s2 = new Student5(222,"Aryan",25);  

    s1.display();  

    s2.display();  

   }  

}  




                                                                 










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