Two StringBuilder​ constructors that take String or CharSequence argument throw a confusing NegativeArraySizeException if the argument is extremely large.

This is because the constructor tries to set the initial capacity equal to the length of the argument + 16 (this is specified in the spec, actually).
When the argument's length is > (Integer.MAX_VALUE - 16), the initial capacity becomes negative due to the integer overflow.

public class T {
    public static void main(String[] args) {
        // 0, 1        -> cannot create str
        // 2, ..., 15  -> confising NegativeArraySizeException
        // 16, 17      -> OOM in StringBuilder
        // 18 and more -> Ok
        int DELTA = 10;

        String str = "Z".repeat(Integer.MAX_VALUE - DELTA);
        StringBuilder sb = new StringBuilder(str);
    }
}

It would be more accurate to throw OutOfMemoryError in such cases.