Java – Constructor Chaining with example

Calling a constructor from the another constructor of same class is known as Constructor chaining. The real purpose of Constructor Chaining is that you can pass parameters through a bunch of different constructors, but only have the initialization done in a single place. This allows you to maintain your initializations from a single location, while providing multiple constructors to the user. If we don’t chain, and two different constructors require a specific parameter, you will have to initialize that parameter twice, and when the initialization changes, you’ll have to change it in every constructor, instead of just the one.

As a rule, constructors with fewer arguments should call those with more

Let’s understand this with the help of an example.

Constructor Chaining Example

In this example, I have several constructors, one constructor is calling another constructor using this keyword.

this() should always be the first statement in constructor otherwise you will get this error message: Exception in thread “main” java.lang.Error: Unresolved compilation problem: Constructor call must be the first statement in a constructor

class Employee
{   
    public String empName;
    public int empSalary;
    public String address;

    //default constructor of the class
    public Employee()
    {
    	//this will call the constructor with String param
        this("Chaitanya");
    }

    public Employee(String name)
    {
    	//call the constructor with (String, int) param
    	this(name, 120035);
    }
    public Employee(String name, int sal)
    {
    	//call the constructor with (String, int, String) param
    	this(name, sal, "Gurgaon");
    }
    public Employee(String name, int sal, String addr)
    {
    	this.empName=name;
    	this.empSalary=sal;
    	this.address=addr;
    }

    void disp() {
    	System.out.println("Employee Name: "+empName);
    	System.out.println("Employee Salary: "+empSalary);
    	System.out.println("Employee Address: "+address);
    }
    public static void main(String[] args)
    {
        Employee obj = new Employee();
        obj.disp();
    }
}

Output:

Employee Name: Chaitanya
Employee Salary: 120035
Employee Address: Gurgaon