Editing Subtyping (section)

===Java===

In Java, '''is-a''' relation between the type parameters of one class or interface and the type parameters of another are determined by the extends and [[Interface (Java)|implements]] clauses.

Using the {{code|Collections}} classes, {{code|ArrayList<E>}} implements {{code|List<E>}}, and {{code|List<E>}} extends {{code|Collection<E>}}. So {{code|ArrayList<String>}} is a subtype of {{code|List<String>}}, which is a subtype of {{code|Collection<String>}}. The subtyping relationship is preserved between the types automatically. When defining an interface, {{code|PayloadList}}, that associates an optional value of [[generic type]] P with each element, its declaration might look like:

<syntaxhighlight lang=java>
interface PayloadList<E, P> extends List<E> {
    void setPayload(int index, P val);
    ...
}
</syntaxhighlight>

The following parameterizations of PayloadList are subtypes of {{code|List<String>}}:

<syntaxhighlight lang=java>
PayloadList<String, String>
PayloadList<String, Integer>
PayloadList<String, Exception>
</syntaxhighlight>