When Does it Make Sense to Use Copy Constructors in Java?

As a Java programmer, it is vital to know when to use the copy constructors in your code. In an interview concerning a Java related job, you are likely to come across a similar question. That’s why we compiled this article to give you an in-depth review of how a copy constructor in Java works.

What is a Copy Constructor?

Before diving deep into explaining when to use them, it is first important to know what copy constructors are. A java copy constructor is a constructor that uses just a single argument that is of a similar kind to the class in which it is implemented. They are widely used in the programming field as a perfect substitute for the clone method which is usually prone to errors.

A copy constructor Java works the same way as in C++ except for the fact that in C++ you will be provided with a default one even if you don’t create one on your own. These types of constructors can be easily implemented as compared to the clone method.

Copy Constructors in Java Script

When Should We Use Copy Constructors?

Consider a case where you are given two accessor methods belonging to a class ‘SampleClass’ as shown in the example below:

public class Employee
{
public String getID()
{
return personalID;
}

public Month getMonth()
{
return new Month (vacationMonth);
}
}

In this block of code, it is assumed that the vacationMonth is a private instance variable of the main class ‘Month’ and personalID is a private instance variable belonging to the string Employee. Note that the copy constructor java is applied to the second method. In this section, you will learn why that is done and why the copy constructor is even employed at all.

The use of a copy constructor in the definition getMonth causes an entirely separate object to be created. The new object has the same values stored in the instance variable as the first vacationMonth object, but with a personal address space. That makes the initial vacationMonth secure.

In the getID method defined in the first accessor method above, a copy constructor java isn’t applied and could be prone to the same problem. However, it doesn’t need a copy constructor because the value of the instance variable personalID cannot be altered whatsoever even if it is made a reference point. That is so because the string Employee is an immutable class which implies it has mutator methods that restrict changing of any string object. Since ‘personalID’ ID cannot be modified, it is safe to return a reference to it despite being a private instance variable.

A java copy constructor can help create a different object that is a duplicate of the object that it embodies as a parameter. However, the newly established copy is, in fact, independent of the original object based on the fact that the location address in the memory is also changed.

The above discussion shows you when to and when not to use the copy constructors Java. Apply the same line of thought in the interview, and you will ace it. You can share your thoughts on this at any time.