In this article, we will go through parameterized constructor in detail

1. Parameterized Constructor :

• A constructor which takes one or more arguments is known as parameterized constructor

Employee.java

package in.bench.resources.constructor.example;

public class Employee {

	// member variables
	int employeeId;
	String employeeName;

	// parametrized constructor
	Employee(int id, String name) {
		System.out.println("Employee class >> Inside parametrized constructor\n");
		this.employeeId = id;
		this.employeeName = name;

	}

	// display() method
	void display() {
		System.out.println("display() method is invoked");
	}

	// main() method - entry point to JVM
	public static void main(String args[]) {
		Employee emp = new Employee(19, "Rahul Dravid");
		emp.display();
	}
}

Output:

Employee class >> Inside parametrized constructor

display() method is invoked

Explanation :

• Here in this example, Employee object is created using below line of code
  Employee emp = new Employee(19, “Rahul Dravid”);
• Which invokes 2-parameter constructor and prints the message inside parameterized constructor with two arguments (int, String)
• And then using object ‘emp’ created, invokes member method display() which prints the message inside method
• So basically depending on number of arguments constructor takes, accordingly we need to pass those number of parameters while constructing the object
• Otherwise will end with compilation error

Let us move on and tweak the above code to see execution results

2. Compilation error scenario:

• In Employee class, there is one 2-argument constructor
• Example: Try to construct an object using below line of code which results compilation error
  Employee emp = new Employee();
• Reason: There is no default constructor defined in class

3. Twist :

• Wait, earlier we discussed that compiler inserts default no-arg constructor during compilation when we are discussing about default constructor with example

Q) So, why compiler doesn’t inserts any default constructor in this case ?

• Compiler inserts default constructor only when there is no constructor defined inside class either it is default or parameterized constructor
• Since this example already got a 2-argument parameterized constructor defined so compiler doesn’t inserts any default constructor

Q) What we can do for successful compilation ?

• Have one more constructor with zero arguments that is default constructor

Q) Is it okay to have more than one constructor inside class ?

• Absolutely, it is fine to have more than one constructor inside class

Q) So, we can overload constructor similar to methods ?

• Of course, we can overload constructor depending on the business requirements similar to method overloading
• But constructor overloading is different comparing with method overloading
• Read more on constructor overloading here

Q) Is overriding also possible ?

• Constructor doesn’t support inheritance concept and therefore no point of overriding constructor or
• In simple words, constructor overriding is not possible

In the following article, we will discuss in detail about constructor overloading concept

Related Articles:

• Java Constructor with example
• Default constructor
• Default constructor v/s Parameterized constructor
• Constructor overloading
• Constructor chaining
• Constructor v/s Methods

Happy Coding !!
Happy Learning !!