What does the -> <- operator do?
I recently came upon the following code:
IntPredicate neg = x -> x <- x;
What is this, some sort of reverse double lambda?
Solution 1:
There is no -> <-
operator. That first ->
is just lambda syntax, as introduced in Java 8, and that second <-
is a misleading concatenation of 'smaller than' <
and 'unary minus' -
.
You can read it as IntPredicate neg = (x) -> (x < (-x));
, i.e. it tests whether x
is smaller than -x
, which is the case for all (well, most) negative numbers, hence the name neg
.
IntPredicate neg = x -> x <- x;
System.out.println(neg.test(4)); // false
System.out.println(neg.test(0)); // false
System.out.println(neg.test(-4)); // true
Just for completeness: This test is not only (intentionally?) hard to understand, but -- as pointed out in the comments -- it also fails for Integer.MIN_VALUE
(which is ==-Integer.MIN_VALUE
). Instead, you should probably just use the much simpler IntPredicate neg = x -> (x < 0);
.