When is a type parameter list required to be provided?

Question

What's the general rule about when a type parameter list is required?

For example, the type parameter list <E> seen between static and the return type Set<E> below: is it required?

public static <E> Set<E> union(Set<E> s1, Set<E> s2) {}

For another example, writing out <E> is not required in the push() or pop() methods below:

public class Stack<E> {
    public Stack();
    public void push(E e);
    public E pop();
}

I don't get your question. If you need a type variable, you need a type parameter list in the generic method. — Sotirios Delimanolis, Mar 16 '14 at 17:05
Is this true for all generic method? include those defined in a generic class? — Zoe, Mar 16 '14 at 17:11
Yes, a generic class does not prevent you from writing a generic method. The types will just be unrelated. — Sotirios Delimanolis, Mar 16 '14 at 17:12
Down vote : user failed to RTFM (read the fine manual / Documents) — alexmac, Mar 16 '14 at 17:12

score 0 · Answer 1 · answered Mar 16 '14 at 17:09

0

maybe this example illustrates how to use the function properly:

public static void main(String[] args) {
    Set<Integer> s1 = new HashSet<>();
    Set<Integer> s2 = new HashSet<>();

    Set<Integer> result = union(s1, s2);
}

public static <E> Set<E> union(Set<E> s1, Set<E> s2) {
    // do something useful here
}

answered Mar 16 '14 at 17:09

oschlueter

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I don't believe that's what the question is about. – Sotirios Delimanolis Mar 16 '14 at 17:10
I have to admit I'm not certain either... ;-) – oschlueter Mar 16 '14 at 17:15

When is a type parameter list required to be provided?

1 Answers1