{"id":4477,"date":"2014-03-30T11:25:37","date_gmt":"2014-03-30T11:25:37","guid":{"rendered":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/concept-of-c-polymorphism-collection-of-common-programming-errors\/"},"modified":"2014-03-30T11:25:37","modified_gmt":"2014-03-30T11:25:37","slug":"concept-of-c-polymorphism-collection-of-common-programming-errors","status":"publish","type":"post","link":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/concept-of-c-polymorphism-collection-of-common-programming-errors\/","title":{"rendered":"Concept of C# polymorphism-Collection of common programming errors"},"content":{"rendered":"
\n

Use ‘new’ modifier, which function will be called is determined when it is compiled.The program will choose the object’s declared type to call its function.(As above, the f’s declared type is father ,so using ‘new’ modifier make the output to show ‘father’.<\/p>\n<\/blockquote>\n

Not really. The decision is still made at execution time, but the new<\/code> method does not<\/em> override the virtual method in the base class. This is most easily shown by extending your example somewhat:<\/p>\n

using System;\n\nclass Base\n{\n    public virtual void Foo()\n    {\n        Console.WriteLine(\"Base.Foo\");\n    }\n}\n\nclass Derived : Base\n{\n    public override void Foo()\n    {\n        Console.WriteLine(\"Derived.Foo\");\n    }\n}\n\nclass MoreDerived : Derived\n{\n    public new void Foo()\n    {\n        Console.WriteLine(\"MoreDerived.Foo\");\n    }\n}\n\nclass Test\n{\n    static void Main()\n    {\n        Base x = new MoreDerived();\n        x.Foo(); \/\/ Prints Derived.Foo\n    }\n}\n<\/code><\/pre>\n
Here, at compile time<\/em> the decision is made to call the most overridden implementation of Base.Foo<\/code> – if there were multiple Foo<\/code> signatures, the decision about which signature to use would be taken, for example. Which implementation will be “the most overridden” is unknown at this point, of course.<\/p>\n
At execution time<\/em>, the CLR will find that most overridden implementation based on the actual type of the target object – which is MoreDerived<\/code>. But MoreDerived.Foo<\/code> doesn’t override Base.Foo<\/code>… whereas Derived.Foo<\/code> does, so the implementation in Derived<\/code> is the one which is actually executed.<\/p>\n","protected":false},"excerpt":{"rendered":"
Use ‘new’ modifier, which function will be called is determined when it is compiled.The program will choose the object’s declared type to call its function.(As above, the f’s declared type is father ,so using ‘new’ modifier make the output to show ‘father’. Not really. The decision is still made at execution time, but the new […]<\/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-4477","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4477","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=4477"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4477\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=4477"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=4477"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=4477"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}