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Java generics generate only one compiled version of a generic class or function regardless of the number of parameterizing types used. Furthermore, the Java run-time environment does not need to know which parameterized type is used because the type information is validated at compile-time and is not included in the compiled code.
Although similar to generics in Java, .NET generics do not apply type erasure, [26]: 208–209 but implement generics as a first class mechanism in the runtime using reification. This design choice provides additional functionality, such as allowing reflection with preservation of generic types, and alleviating some of the limits of erasure ...
In effect, each definition of a generic class also makes available interfaces for the covariant and contravariant parts of that class. Java provides use-site variance annotations through wildcards , a restricted form of bounded existential types .
If a class does not specify its superclass, it implicitly inherits from java.lang.Object class. Thus all classes in Java are subclasses of Object class. If the superclass does not have a constructor without parameters the subclass must specify in its constructors what constructor of the superclass to use. For example:
In class-based object-oriented programming, abstract types are implemented as abstract classes (also known as abstract base classes), and concrete types as concrete classes. In generic programming, the analogous notion is a concept, which similarly specifies syntax and semantics, but does not require a subtype relationship: two unrelated types ...
In the Java programming language, the wildcard? is a special kind of type argument [1] that controls the type safety of the use of generic (parameterized) types. [2] It can be used in variable declarations and instantiations as well as in method definitions, but not in the definition of a generic type.
Typically a generic function is an instance of a class that inherits both from function and standard-object. Thus generic functions are both functions (that can be called with and applied to arguments) and ordinary objects. The book The Art of the Metaobject Protocol explains the implementation and use of CLOS generic functions in detail.
Generic function, a computer programming entity made up of all methods having the same name; Generic programming, a computer programming paradigm based on method/functions or classes defined irrespective of the concrete data types used upon instantiation Generics in Java