Find the most repeating character in a string

Following snipper will return most repeated character in a string

public char getMax(String str) {

    char maxChar = ' ';

    int maxCnt = 0;

    char [] charmax = new char[Character.MAX_VALUE+1];

    for(int i = str.length()-1; i>=0; i--) {

        char ch = str.charAt(i);

        int num = ++charmax[ch];

        if(num >= maxCnt) {

            maxCnt = charmax[ch];

            maxChar = ch;

        }

    }

    return maxChar;

}