Still Don't Get The Difference Between “Overloading and Overriding"

You should also consider giving DMAS rule a quick look, it explains how to resolve the equation to get correct answer!

Operator overloading on the other hand is (but not restrained to be) performed for custom classes and objects. A very common example of such cases and learning techniques is the complex numbers class. Complex numbers have a real and an imaginary part, operator overloading is required to work around with addition, multiplication and other operations. So, for example, you can use a complex number object to work around with your operator overloading skills.

An example here would be to show how to add two Program classes in C#:
The above program has an overloaded operator, which returns a string message (see the function signature) “Added” each time you add two Program objects. That is just to show you, that operators also, when overloaded, allow you to perform the functions that you want to! You can return multiple results, such as array of results or you can pass another message, or like talked about complex numbers, you can return another complex number after the operation. In C# overloaded operators are static, so that is why I provided that keyword in the signature. Rest is the body for the function, where I am only returning a string-literal.

Still got questions?

Well if you still have some questions, I have some answers for them. My apologies if I can still not satisfy your needs. This is not a TL;DR.

1. Is it really required?

No, it is not required, but is provided as per your need. Whenever you need to overload your functions to allow multiple arguments or different arguments under the same process. You can use (function) overloading. Also, if your objects require arithmetic operations, addition or subtraction, you can overload the operators provided in the language also. Almost every OOP or widely used programming language supports operator overloading.

Note: Java and C do not support operator overloading. Java is an example of OOP language not supporting operator overloading, and C is a widely used programming language that doesn’t support operator overloading.

2. How does it work? (Applies to function overloading)

Overloading is worked out by compiler itself, it makes a choice based on the formal parameters passed to the function. There can be implicit casting that can take place to find a suitable function to handle the call.

Let us compile a few examples and see what happens:
In the above cases, all of the functions are mapped to their representative function calls based on their parameters. First one gets called for the one that accepts a character, then a double (float can be casted to double and so on) and then comes a string later is the integer value. All of these choices were made by the compiler to detect which one to execute; based on the formal parameters being passed.

Off-record: I am waiting for more questions to be added to the list, if you have one, let me know.

What is overriding?

Just as we noticed a few things about overloading, we should consider learning the same things about overriding also. Let us break the concept into pieces and see what does it have for us and why should we use it anyway. Override, ever heard the same English term in a movie? If you are an Avengers fan of a same military-like movie fan or same, such as Interstellar ( I loved that movie), you must have heard them saying, “override” to some command that machine was talking about. We are talking about the same “override” function here. Google says,

Definition of “override” by Google

In the above definition-list, we will find our interest in the second definition. “interrupt the action of (an automatic device), typically in order to take manual control.” Once again, Google has explained the term override and we can understand it in our general-programming concepts. Indeed overriding is used to overcome the default behavior of a function in our objects and APIs. So that we can enforce our own implementations for the process. In the coming sections, I will show you how to override the default behaviors and functions in languages; C# and C++ are to be taken into concern, Java and others can also be implemented but with a little modification as was in the case of operator overloading.

Object-oriented programming languages provide us with a function to inherit from base classes. In this post, I won’t share the inheritance concepts, but you should consider giving it a thorough look before moving forward. The inherited functions and other stuff is passed down to the child object, thus allowing it to perform the same functions as the previous one did.
Now, we know that we can define functions which can be passed down to the next, as they are generally. The Son object can also walk and so on. Where is the overloading then? The overloading comes, when Son performs a different action, or overrides the default behavior that was performed for a long time by the base classes; was intended to be performed.

So, for example in a carpenter’s family if father’s job was as a carpenter and somehow son doesn’t like that job and wants to be a football player, he can easily override that and perform his own actions. Like this:
In the above code, there were two tag marks added. One of them to the father and other to the son. The tag mark of “virtual” meant, that this can be overriden. So Father object does allow the derived objects to perform a different action, and child if interested in, can perform a different action or can maintain the family occupation and serve as a carpenter. The keyword “virtual” (or “abstract”; explained later) is required in order to override the default behavior in derived objects. It is just to change the implementation of a procedure.

Question and answer session:

1. What are virtual and abstract keywords?
   
   These keywords are used to identify the functions that can be overridden. Abstract is somewhat a different story and it takes you back to the inheritance and the concept about concrete and abstract classes and etc. I am not interested in confusing you for those topics here.
   
   Long story short, virtual is applied to the functions, that can be overridden.
   
   
2. Any real world implementation?
   
   Yes, if you are a C# programmer you would have noticed (and known) that object is the base class for every managed type. In a C# program, when you call the .ToString function (where does that come from? See the first code sample in this overriding section) the program itself returns the full type name for it. For example,
   
   1. using System;
   3. namespace Example {
   4. class Program {
   5. static void Main(string[] args) {
   6. // Our very basic Console app.
   7. Console.WriteLine(
   8. new Program()
   9. );
   10. }
   11. }
   12. }
   14. // Output:
   15. // Example.Program
   Which is the type name for the class object. Now, for example if you have a class that holds the data for the users. You don’t have to create a separate function to display the details for a user, you can override the function and change its implementation for your class.
   
   1. class User {
   2. public string Name { get; set; }
   3. public int Age { get; set; }
   5. public override string ToString() {
   6. return string.Format("Name: {0}, Age: {1}", this.Name, this.Age);
   7. }
   8. }
   The above code, when called as:
   
   1. var user = new User
   2. {
   3. Name = "Afzaal Ahmad Zeeshan",
   4. Age = 20
   5. };
   7. Console.WriteLine(user);
   Would provide you with the following output:
   
   Name: Afzaal Ahmad Zeeshan, Age: 20
   
   Pretty easy isn’t it? We have no overridden the default behavior of object’s ToString function. You can in a similar manner, override other functions and procedures as required.

Points of Interest

This post would be much beneficial to those who don’t understand the concept of overloading and overriding and their common difference. This post aims at them, to teach them the difference. I hope by now you must have understand the common difference of them.

If you still get confused over something, or you have another question for them, do let me know and I will update the post for future readers. Finally, a graphical difference of overloading and overriding is:



Illustration of the difference.