Constructors & its Types

Constructors & its Types

• 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: 
• 1. No argument constructor or Default constructor
• 2. Arguments constructor
• Rules for creating Java constructor
• Constructor name must be the same as its class name.
• A Constructor must have no explicit return type.
• A Java constructor cannot be abstract, static, final, and synchronized.

1.0 No constructor created.

• Java automatically created default constructor.
• It is automatically called when objects are created.
• Full Example:
  

1.1 No argument constructor or Default constructor (without values)

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

class_name()
{
}

• Example:

 MCA2()
    {
        System.out.println("Constructor created.");
    }

• Full Example:
  

1.2 No argument constructor or Default constructor (with values)

• The default constructor is used to provide the default values to the object like 0, null, etc., depending on the type.
• Syntax:

class_name()
{
//display default values of members variable
}

• Example:

MCA2()
    {
        System.out.println("Constructor created.");
        System.out.println(rollno);
        System.out.println(name);
    }

• Full Example:
  

2.0 Arguments or Parameterized Constructor

• A constructor which has a specific number of parameters is called a parameterized constructor.
• Why?
• The parameterized constructor is used to provide different values to distinct objects. 
• However, you can provide the same values also.
• Syntax:

class_name(agruments)

{

}

• Example:

MCA2(int rollno, String name)

{

System.out.println(rollno);

System.out.println(name);

}

How to pass arguments to constructors in main() method?

MCA2 r1 = new MCA2(101,"Sarthak");

3.0 Overloading Constructor

• Constructors can also be overloaded. 
• Constructor overloading is a concept of having more than one constructor with different parameters list.
• Each constructor is calling according to its signature matching.
• For e.g. MCA2 class has 3 types of constructors. 
• Full Example:
  

Constructor Vs Method