Method (computer programming): Difference between revisions

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A '''method''' in [[object-oriented programming]] (OOP) is a [[Procedure (computer science)|procedure]] associated with a [[Message passing|message]] and an [[Object (computer science)|object]]. An object is mostly made up of data and behavior, which form the interface that an object presents to the outside world. Data is represented as [[Property (programming)|properties]] of the object and behavior as methods. For example, a <code>Window</code> object would have methods such as <code>open</code> and <code>close</code>, while its state (whether it is opened or closed) would be a property.

In [[class-based programming]], methods are defined in a [[class (computer science)|class]], and objects are instances of a given class. One of the most important capabilities that a method provides is method overriding. The same name (e.g., <code>area</code>) can be used for multiple different kinds of classes. This allows the sending objects to invoke behaviors and to delegate the implementation of those behaviors to the receiving object. MethodA method in Java programming sets the behaviourbehavior of a class object. For example, an object can send an <code>area</code> message to another object and the appropriate formula is invoked whether the receiving object is a <code>rectangle</code>, <code>circle</code>, <code>triangle</code>, etc.

Methods also provide the interface that other classes use to access and modify the data [[Property (programming)|properties]] of an object. This is known as encapsulation. Encapsulation and overriding are the two primary distinguishing features between methods and procedure calls.<ref>{{cite web|title=What is an Object?|url=http://docs.oracle.com/javase/tutorial/java/concepts/object.html|work=oracle.com|publisher=Oracle Corporation|accessdate=13 December 2013}}</ref>

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[[Method overriding]] and overloading are two of the most significant ways that a method differs from a conventional procedure or function call. Overriding refers to a subclass redefining the implementation of a method of its superclass. For example, <code>findArea</code> may be a method defined on a shape class. The various subclasses: <code>rectangle</code>, <code>circle</code>, <code>triangle</code>, etc. would each define the appropriate formula to calculate their area. The idea is to look at objects as "black boxes" so that changes to the internals of the object can be made with minimal impact on the other objects that use it. This is known as encapsulation and is meant to make code easier to maintain and re-use.

Method overloading, on the other hand, refers to differentiating the code used to handle a message based on the parameters of the method. If one views the receiving object as the first parameter in any method then overriding is just a special case of overloading where the selection is based only on the first argument.<ref>[http://www.codeproject.com/Articles/16407/METHOD-Overload-Vs-Overriding http://www.codeproject.com/Articles/16407/METHOD-Overload-Vs-Overriding]</ref> The following simple [[Java language|Java]] example illustrates the difference:<ref>{{cite web

| accessdate = 2011-08-12

| author = John Suzuki

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| publisher = j Guru

| title = What is an overloaded method?

| quote = Overloaded methods are multiple methods in the same class that shareshares the same name but have different parameter lists. Overloaded methods cannot have the same parameter lists with different return types.

| url = http://www.jguru.com/faq/view.jsp?EID=15565}}

</ref>

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===Constructors===

A [[Constructor (computer science)|''constructor'']] is a method that is called at the beginning of an object's lifetime to create and initialize the object, a process called [[object creation|construction]] (or ''instantiation''). Initialization may include an acquisition of resources. Constructors may have parameters but usually, do not return values in most languages. See the following example in Java:

<syntaxhighlight lang="java">

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==Class methods==

Class methods are methods that are called on a [[Class (computer programming)|class]] rather than an instance. They are typically used as part of an object [[meta-model]]. I.e, for each class, defined an instance of the class object in the meta-model is created. [[Meta-object protocol|Meta-model protocols]] allow classes to be created and deleted. In this sense, they provide the same functionality as constructors and destructors described above. But in some languages such as the [[Common Lisp Object System|Common Lisp Object System (CLOS)]] the meta-model allows the developer to dynamically alter the object model at run time: e.g., to create new classes, redefine the class hierarchy, modify properties, etc.

==Special methods==