问题
The anyMatch operation will return true if it finds an element - the noneMatch operation will return false it if finds a matching element.
The anyMatch operation will return false if it finds no matching element - the noneMatch operation will return true if finds no matching element.
Therefore, instead of having both of these operations, could we not just do with one, or am I missing something? In essence, anyMatch returning false is a way of evaluating the truth of noneMatch's predicate.
回答1:
Same reason you have a != b, instead of only supporting ! (a == b):
- Easy of use.
- Clarity of purpose.
回答2:
Yes, we totally could. There's at least a moderately reasonable reason for it, though: the ! would go at the very beginning of a stream expression that could be chained many lines long, e.g. you'd have to write
!collection.stream()
.map(someMapFunction)
.filter(someFilterFunction)
.distinct()
.sorted(myComparator)
.map(someOtherMapFunction)
.filter(someOtherFilterFunction)
.anyMatch(somePredicate)
...and by the time you've reached the anyMatch when you're reading the code, the negation at the beginning is harder to remember.
(For what it's worth, the JDK generally seems to have a lot fewer redundant methods than other languages I could name.)
来源：https://stackoverflow.com/questions/35092455/java-stream-purpose-of-having-both-anymatch-and-nonematch-operations