Editing Java (programming language) (section)

=== Generics ===
{{Main|Generics in Java}}

In 2004, [[generic programming|generics]] were added to the Java language, as part of J2SE 5.0. Prior to the introduction of generics, each variable declaration had to be of a specific type. For container classes, for example, this is a problem because there is no easy way to create a container that accepts only specific types of objects. Either the container operates on all subtypes of a class or interface, usually <code>Object</code>, or a different container class has to be created for each contained class. Generics allow compile-time type checking without having to create many container classes, each containing almost identical code. In addition to enabling more efficient code, certain runtime exceptions are prevented from occurring, by issuing compile-time errors. If Java prevented all runtime type errors (<code>ClassCastException</code>s) from occurring, it would be [[type safety|type safe]].

In 2016, the type system of Java was proven [[soundness|unsound]] in that it is possible to use generics to construct classes and methods that allow assignment of an instance of one class to a variable of another unrelated class. Such code is accepted by the compiler, but fails at run time with a class cast exception.<ref>{{cite web|url=https://raw.githubusercontent.com/namin/unsound/master/doc/unsound-oopsla16.pdf|title=Java and Scala's Type Systems are Unsound|access-date=February 20, 2017 |archive-url=https://web.archive.org/web/20161128174902/https://raw.githubusercontent.com/namin/unsound/master/doc/unsound-oopsla16.pdf |archive-date=November 28, 2016|url-status=live}}</ref>