Regular Expression Match Groups

import java.util.ArrayList;
import java.util.List;

public class App {

    public final char S = '(';
    public final char E = ')';
    public final char X = '\\';

    /**
     * Actual Output:
     *    Groups: [(//), (\d{1,2}), (\d{1,2}), (\d{2,4})]
     * Expected Output:
     *    Groups: [\\b((\\d{1,2})/(\\d{1,2})/(\\d{2,4}))\\b, ((\\d{1,2})/(\\d{1,2})/(\\d{2,4})), (\d{1,2}), (\d{1,2}), (\d{2,4})]
     */

    public App() {
        String expression = "\\b((\\d{1,2})/(\\d{1,2})/(\\d{2,4}))\\b";

        List<String> groups = findGroups(expression);

        System.out.println("Groups: " + groups);
    }

    public List<String> findGroups(String expression) {
        List<String> groups = new ArrayList<>();
        int[] pos;
        int start;
        int end;
        String sub;
        boolean done = false;

        while (expression.length() > 0 && !done) {
            pos = scanString(expression);
            start = pos[0];
            end = pos[1];

            if (start == -1 || end == -1) {
                done = true;
                continue;
            }

            sub = expression.substring(start, end);
            expression = splice(expression, start, end);
            groups.add(0, sub);
        }

        return groups;
    }

    public String splice(String str, int start, int end) {
        String first = str.substring(0, start);
        String last = str.substring(end, str.length());
        return first + last;
    }

    public int[] scanString(String str) {
        int[] range = new int[] { -1, -1 };
        int min = 0;
        int max = str.length() - 1;
        int start = min;
        int end = max;
        char curr;

        while (start <= max) {
            curr = str.charAt(start);
            if (curr == S) {
                range[0] = start;
            }
            start++;
        }

        end = range[0];

        while (end > -1 && end <= max) {
            curr = str.charAt(end);
            if (curr == E) {
                range[1] = end + 1;
                break;
            }

            end++;
        }

        return range;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        new App();
    }
}