What are some quirks of the Java compiler?

Question

IntelliJ has an inspection setting to warn you of "Javac quirks" that might affect your code, but I have yet to come across any. What are some of these quirks, either recognized by IntelliJ or in general?

Answer 1

I've just seen "Use of '_' as a lambda parameter name is not allowed" (IntelliJ IDEA CE 14.0.2).

public static <T> BinaryOperator<T> toLastElement() {
    return (_, current) -> current;
}