Since String.split() uses regular expressions to split, you could do something like this:
String[] nos = "-1000--1".split("(?<=\\d)-";
This means you split at minus characters that follow a digit, i.e. must be an operator.
Note that the positive look-behind (?<=\d) needs to be used since you only want to match the minus character. String.split() removes all matching separators and thus something like \d- would remove digits as well.
To parse the numbers you'd then iterate over the array elements and call Integer.valueOf(element) or Integer.parseInt(element).
Note that this assumes the input string to be valid. Depending on what you want to achieve, you might first have to check the input for a match, e.g. by using -?\d--?\d to check whether the string is in format x-y where x and y can be positive or negative integers.