How does Java know which String::compareTo
method reference to use when calling Collections.sort(someListOfStrings, String::compareTo);
? compareTo
is not static and it needs to know the value
of the "left hand side" of the comparison.
Suppose that you use method reference for Comparator
interface:
Comparator<String> cmp = String::compareTo;
When you call the cmp.compare(left, right)
(which is "single abstract method" or "SAM" of Comparator
interface), the magic occurs:
int result = cmp.compare(left, right);
| |
/------------------------/ |
| /---------------/
| |
left.compareTo(right);
Basically all the parameters of SAM are converted to the parameters of the referred method, but this
object (which is on the left side) is also counted as parameter.
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