C# got it wrong. Java got it right.<\/p>\n
C# doesn’t let you “seal” methods that aren’t overridden. Java allows you to mark any method as “final” – whether it’s an overridden method or not. This subtle detail has interesting implications.<\/p>\n
The Gang of Four’s “Design Patterns: Elements of Reusable Object-Oriented Software<\/a>” was published in 1994—many years before C# was first released and just two years before Java was released. (Although, most of the code in the book was presented in C++.) The book presents the “Template Method” behavioral pattern. Template methods define the “framework” of an algorithm and leave subclasses to define the behavior. Unfortunately, if you cannot mark a template method as ‘final’ (or ‘sealed’ in C#), it enables subclasses to—potentially by accident—change the behavior of the template method.<\/p>\n Here’s a template method in action, written in JS++, to demonstrate how this might be undesirable:<\/p>\n In the above class, the template method (“save”) is marked as ‘final’. Without ‘final’, an overriding method (or overwriting method, to use JS++ terminology) can potentially forget to perform business object validation before altering the database. This can lead to potential bugs and security threats.<\/p>\n Beginning with the next release of JS++, you will be able to mark any method as ‘final’.<\/p>\n","protected":false},"excerpt":{"rendered":" C# got it wrong. Java got it right. C# doesn’t let you “seal” methods that aren’t overridden. Java allows you to mark any method as “final” – whether it’s an overridden method or not. This subtle detail has interesting implications. The Gang of Four’s “Design Patterns: Elements of Reusable Object-Oriented Software” was published in 1994—many … Continue reading “Design Patterns: The Template Method Pattern and Final Methods”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[3,2],"tags":[],"_links":{"self":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/483"}],"collection":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/comments?post=483"}],"version-history":[{"count":6,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/483\/revisions"}],"predecessor-version":[{"id":1253,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/483\/revisions\/1253"}],"wp:attachment":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/media?parent=483"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/categories?post=483"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/tags?post=483"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\r\nabstract class Model\r\n{\r\n\tabstract public bool validate();\r\n\tabstract protected void saveTemplate(IDatabase db);\r\n\tpublic final void save(IDatabase db) {\r\n\t\tif (!this.validate()) {\r\n\t\t\tthrow new ValidationException();\r\n\t\t}\r\n\r\n\t\tthis.saveTemplate(db);\r\n\t}\r\n}\r\n<\/pre>\n