Java String count shared characters between two String values

//package com.demo2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String str = "demo2s.com demo2s.com";
        String chars = "com";
        System.out.println(numSharedChars(str, chars));
    }/* w  w  w  . ja va 2 s .  co  m*/

    /**
     * Counts the number of (not necessarily distinct) characters in the
     * string that also happen to be in 'chars'
     */
    public static int numSharedChars(final String str, final String chars) {

        if (str == null || chars == null) {
            return 0;
        }

        int total = 0, pos = -1;
        while ((pos = indexOfChars(str, chars, pos + 1)) != -1) {
            total++;
        }

        return total;
    }

    /**
     * Like String.indexOf() except that it will look for any of the
     * characters in 'chars' (similar to C's strpbrk)
     */
    public static int indexOfChars(String str, String chars, int fromIndex) {
        final int len = str.length();

        for (int pos = fromIndex; pos < len; pos++) {
            if (chars.indexOf(str.charAt(pos)) >= 0) {
                return pos;
            }
        }

        return -1;
    }

    /**
     * Like String.indexOf() except that it will look for any of the
     * characters in 'chars' (similar to C's strpbrk)
     */
    public static int indexOfChars(String str, String chars) {
        return indexOfChars(str, chars, 0);
    }
}