Generics and Variance of Types - nus-cs2030/2021-s1 GitHub Wiki
Generics
- Abstraction principle: avoid defining similar methods/classes with duplicate code
- Allows the specification, with a single method/class declaration, of a set of related methods/classes/types
Autoboxing and Unboxing
- Primitives types are not the same as classes and so cannot be used with generics
- Primitives are therefore auto-boxed/unboxed in Java to their corresponding wrapper class
Covariance, contravariance, invariance
| Variance | Meaning |
|---|---|
| Covariant | preserves the ordering of types |
| Contravariant | reverses the ordering of types |
| Invariant | none of the above |
Java Collections Framework (JCF)
- A collection is an object that represents a group of objects
- Since these objects can be of any class, we thus use a generic type to avoid defining similar methods/classes with duplicate code (recall abstraction principle)