regex to match absent groups at fixed locations

A regex is needed that always matches (with matches(), not find()) and always recognizes 3 groups, for 3 different cases of input, like

1. 1234 ab$.5!c=:d6 efg(789)
2. 1234 efg(567)
3. efg(567)

The pattern

(?:^(\d+)\s+(\S)\s)?\s*([^\(]+\(\S+\))

represents the kind of values expected in each group (without assumptions about the location of characters), but only works correctly in case #1, producing

1234, ab$.5!c:d6, efg(789)

For cases 2 and 3, the same pattern does not work, giving, respectively

null, null, ab$.5!c:d6 efg(789)
null, null, efg(789)

Any ideas?

You could use the below regex.

^(?:(\d+)\s+(?:(\S+)\s)?)?([^(]+\([^)]*\))$

DEMO

String s = "1234 efg(567)";
Matcher m = Pattern.compile("^(?:(\\d+)\\s+(?:(\\S+)\\s)?)?([^(]+\\([^)]*\\))$").matcher(s);
while(m.find()) {
    if(m.group(1) != null)
        System.out.println(m.group(1));
    if(m.group(2) != null)
        System.out.println(m.group(2));
    if(m.group(3) != null)
        System.out.println(m.group(3));
}