I'm a bit confused about the syntax of generic methods. My understanding after reading this post was that generic method should be declared like this:
public static <E> void printArray( E[] inputArray )
with <E>
being a placeholder that informs that E is a generic type
So why do I find in the javadoc things like this:
Stream<T> filter(Predicate<? super T> predicate)
No placeholder? I would have expect
<T> Stream<T> filter(Predicate<? super T> predicate)
And why
<R> Stream<R> map(Function<? super T,? extends R> mapper)
This time there is a placeholder, but only for R and not for T. Why?
These methods are instance methods defined on the interface Stream
, which defines the type parameter on the type :
public interface Stream<T> {
Stream<T> filter(Predicate<? super T>)
}
...so the type parameter is defined on the interface, not the method.
As you noticed, type parameters that aren't defined on the interface are defined on a method-by-method basis, in the case of map
.
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