{"id":4501,"date":"2014-03-30T12:09:50","date_gmt":"2014-03-30T12:09:50","guid":{"rendered":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/polymorphism-define-in-just-two-sentences-collection-of-common-programming-errors\/"},"modified":"2014-03-30T12:09:50","modified_gmt":"2014-03-30T12:09:50","slug":"polymorphism-define-in-just-two-sentences-collection-of-common-programming-errors","status":"publish","type":"post","link":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/polymorphism-define-in-just-two-sentences-collection-of-common-programming-errors\/","title":{"rendered":"Polymorphism – Define In Just Two Sentences-Collection of common programming errors"},"content":{"rendered":"

Just thought I’d add my own interpretation of what polymorphism is: very generically, polymorphism is the act of providing a single interface<\/em> to entities of different types<\/em>.<\/p>\n

That’s rather generic, but that’s the only way I can think of to wrap all three types of polymorphisms I know about: ad hoc<\/em>, parametric<\/em> and subtype<\/em>. I’ll go in more details below, and have sorted polymorphism types by name, alphabetically. The one you’re interested on is most probably subtype polymorphism<\/em>, which is the last one.<\/p>\n

ad hoc polymorphism<\/h2>\n

ad hoc polymorphism<\/em> is the act of providing multiple implementations of the same method for different parameter types. In OOP, it’s generally known as method overloading<\/em>. For example:<\/p>\n

public String format(int a) {\n    return String.format(\"%2d\", a);\n}\n\npublic String format(Date a) {\n    return new SimpleDateFormat(\"yyyy-MM-dd'T'HH:mm:ss'Z'\").format(a);\n}\n<\/code><\/pre>\n
Both format<\/code> methods share a single interface<\/em> but work on entities of different types<\/em>.<\/p>\n
Parametric polymorphism<\/h2>\n
Parametric polymorphism<\/em> is the act of making a class (or method) work on a type that is itself a parameter of the class (or method). It’s often referred to as generics<\/em>.<\/p>\n
For example, Java’s List[T]<\/code> expects a parameter T<\/code> at instantiation time, and this parameter defines the type of the resulting object.<\/p>\n
Note for purists that I’m purposefully ignoring raw types<\/em> as I feel they’d just muddy the waters in this context.<\/p>\n
List[String]<\/code> and List[Date]<\/code> share a single interface<\/em>, but work on (and are) different types<\/em>.<\/p>\n
Subtype polymorphism<\/h2>\n
Subtype polymorphism<\/em> is probably what you initially meant in your question: it’s the act of providing a single interface to multiple implementations of the same type.<\/p>\n
To use the customary example: Animal<\/code> provides a contract that all implementations must respect. Dog<\/code> is an Animal<\/code>, and as such supports all operations that Animal<\/code> declares. According to the Liskov substitution principle, this allows you to use an instance of Dog<\/code> where an instance of Animal<\/code> is expected (but not the other way around).<\/p>\n
If Cat<\/code> and Dog<\/code> are both subclasses of Animal<\/code>, then they share a single interface<\/em> but are in fact different types<\/em>.<\/p>\n
I’m going off in a bit of a tangent here, but subtype polymorphism is (I think) the only one that allows overriding<\/em>: the act of redefining the behaviour of a method defined by a parent class. This is often confused with overloading<\/em> which, as we saw before, is a type of polymorphism and doesn’t in fact need subclassing (nor does it need classes, really).<\/p>\n","protected":false},"excerpt":{"rendered":"
Just thought I’d add my own interpretation of what polymorphism is: very generically, polymorphism is the act of providing a single interface to entities of different types. That’s rather generic, but that’s the only way I can think of to wrap all three types of polymorphisms I know about: ad hoc, parametric and subtype. I’ll […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4501","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4501","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=4501"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4501\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=4501"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=4501"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=4501"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}