Function overloading or method overloading is a feature found in various programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
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C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
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Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
that allows the creation of several methods with the same name which differ from each other in terms of the type of the input and the type of the output of the function.
For example, doTask and doTask(object O) are overloaded methods. To call the latter, an object
Object (computer science)
In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....
, whereas the former does not require a parameter, and is called with an empty parameter field. A common error would be to assign a default value to the object in the second method, which would result in an ambiguous call error, as the compiler wouldn't know which of the two methods to use.
Another appropriate example would be a Print(object O) method. In this case one might like the method to be different when printing, for example, text or pictures. The two different methods may be overloaded as Print(text_object T); Print(image_object P). If we write the overloaded print methods for all objects our program will "print", we never have to worry about the type of the object, and the correct function
Subroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
call again, the call is always: Print(something).
Method overloading is usually associated with statically-typed programming languages which enforce type checking in function calls. When overloading a method, you are really just making a number of different methods that happen to have the same name. It is resolved at compile time
Compile time
In computer science, compile time refers to either the operations performed by a compiler , programming language requirements that must be met by source code for it to be successfully compiled , or properties of the program that can be reasoned about at compile time.The operations performed at...
In object-oriented programming, a virtual function or virtual method is a function or method whose behaviour can be overridden within an inheriting class by a function with the same signature...
s, where the correct method is chosen at runtime.
Constructor overloading
Constructors, used to create instances of an object, may also be overloaded in some object oriented programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
s. Because in many languages the constructor’s name is predetermined by the name of the class, it would seem that there can be only one constructor. Whenever multiple constructors are needed, they are implemented as overloaded functions. A default constructor takes no parameters, instantiating the object members
Instance variable
In object-oriented programming with classes, an instance variable is a variable defined in a class , for which each object of the class has a separate copy. They live in memory for the life of the object....
with a value zero. For example, a default constructor for a restaurant bill object written in C++ might set the Tip to 15%:
Bill
{
tip = 15.0;
total = 0.0;
}
The drawback to this is that it takes two steps to change the value of the created Bill object. The following shows creation and changing the values within the main program:
Bill cafe;
cafe.tip = 10.00;
cafe.total = 4.00;
By overloading the constructor, one could pass the tip and total as parameters at creation. This shows the overloaded constructor with two parameters:
Bill(double setTip, double setTotal)
{
tip = setTip;
total = setTotal;
}
Now a function that creates a new Bill object could pass two values into the constructor and set the data members in one step. The following shows creation and setting the values:
Bill cafe(10.00, 4.00);
This can be useful in increasing program efficiency and reducing code length.
Caveats
If a method is designed with an excessive number of overloads, it may be difficult for developers to discern which overload is being called simply by reading the code. This is particularly true if some of the overloaded parameters are of types that are inherited types of other possible parameters (for example "object"). An IDE that can do the overload resolution and display (or navigate to) the correct overload can resolve this issue.
The factory method pattern is an object-oriented design pattern to implement the concept of factories. Like other creational patterns, it deals with the problem of creating objects without specifying the exact class of object that will be created.The creation of an object often requires complex...
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
In object-oriented programming, a constructor in a class is a special type of subroutine called at the creation of an object. It prepares the new object for use, often accepting parameters which the constructor uses to set any member variables required when the object is first created...
In computer science, abstraction is the process by which data and programs are defined with a representation similar to its pictorial meaning as rooted in the more complex realm of human life and language with their higher need of summarization and categorization , while hiding away the...
In computer science, dynamic dispatch is the process of mapping a message to a specific sequence of code at runtime. This is done to support the cases where the appropriate method can't be determined at compile-time...
In object oriented computer programming, operator overloading—less commonly known as operator ad-hoc polymorphism—is a specific case of polymorphism, where different operators have different implementations depending on their arguments...
Method signature
External links
Bertrand Meyer: Overloading vs Object Technology, in Journal of Object-Oriented Programming (JOOP), vol. 14, no. 4, October-November 2001, available online
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