Pattern Troubles

I have a Java pattern I would like to match. I want to take my initial pattern an match the first occurrence of it. However, I consider

public static void main(String[] args)
    {
        final String expression = "(\\s*(a{1}\\s*b{1})\\s*)";

        Scanner scanner1 = new Scanner(" ab");
        //should be rejected
        Scanner scanner2 = new Scanner开发者_开发问答("cab");

        System.out.println(scanner1.findWithinHorizon(expression, 0));
        System.out.println(scanner2.findWithinHorizon(expression, 0));
    }

When I run the above code, I get the following output:

ab
ab

I've tried modifying the pattern to use reluctant and possessive quantifiers, but neither seem to produce the results I expect. What am I doing wrong here?

I assume you want to only match " ab" and not "cab" or "c ab", so use this regex to start at the beginning of the string: final String expression = "^(\\s*(a{1}\\s*b{1})\\s*)";

If you want to also match "c ab" but not "cab" try this: final String expression = "((?<!\\w)\\s*(a{1}\\s*b{1})\\s*)";