遍历String字符串，得到出现次数最多的字母

//There is no need to explain the code right?

package com.hp.test;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class CharacterCheck {

    public static void main(String[] args) {
        String str = "sdfwefwefp[kmlskdjfowefjowefnsdlkj";
        char ca[] = str.toCharArray();
        Map<Character, Integer> charMap = new HashMap<Character, Integer>();
        int maxNum = 1;
        for(char c : ca){
            if(charMap.containsKey(c)){
                int preNum = charMap.get(c);
                charMap.put(c, preNum + 1);
                if(maxNum < (preNum + 1)){
                    maxNum = maxNum + 1;
                }
            } else {
                charMap.put(c, 1);
            }
        }
        
        Set<Character> keys = charMap.keySet();
        for(char c : keys){
            if(charMap.get(c) == maxNum){
                System.out.println(c + " show up for " + charMap.get(c) + " times, is the biggest!");
            } else {
                System.out.println(c + " show up for " + charMap.get(c) + " times!");
            }
        }
    }
}