Java regular expression to identify strings with more digits than non-digits

That's not a regular language, and thus it cannot be captured by a vanilla regex. It may be possible anyway, but it will almost certainly be easier not to use a regex:

public static boolean moreDigitsThanNonDigits(String s) {
    int diff = 0;
    for(int i = 0; i < s.length(); ++i) {
        if(Character.isDigit(s.charAt(i))) ++diff;
        else --diff;
    }
    return diff > 0;
}

You won't be able to write a regexp that does this. But you already said you're using Java, why not mix in a little code?

public boolean moreDigitsThanNonDigits(String input) {
    String nonDigits = input.replace("[0-9]","");
    return input.length() > (nonDigits.length * 2);
}

Regular expressions are conceptually not able to preform such a task. They are equivalent to formal languages or (regular) automatons. They have no notion of memory (or a stack), so they cannot count the occurences of symbols. The next extension in terms of expressiveness are push-down automatons (or stack machines), which correspond to context free grammars. Before writing such a grammer for this task, using a method like the moreDigitsThanNonDigits above would be appropriate.

As already mentioned the language in question is not regular and cannot be detected using a regular expression.

I'll give you one more way of counting the number of digits and number of non-digits in a string using regex!!

You can use the String.replaceAll method to delete all non-digits in the input string. The length of the resultant string will be the number of digits in the input.

Similarly you can delete all the digits in the input string and the length of the resultant string will be the number of non-digits in the input string.

public static boolean test(String str) {
         int numDigits = str.replaceAll("\\D","").length();
         int numNonDigits = str.replaceAll("\\d","").length();

         return numDigits > numNonDigits;
}

Ideone Link

I'm not sure that using regular expressions would be the best solution here.

regex alone can't (since they don't count anything); but if you want to use them then just use two replacements: one that strips out all the digits and one that only keeps them. then compare string lengths of the results.

of course, i'd rather use Dave's answer.