import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class FrequencyFinder {

	public static void main(String[] args) {
		String str = "aaabbbaaacccc     aaaaddddd";
		findSecondHighestFreq(str);
	}
	
	private static char findSecondHighestFreq(String inStr) {
		char secondChar = 0;
		Map<Character, Integer> charMap = new HashMap<Character, Integer>();
		scanChar(inStr.toCharArray(), charMap);
		
		List<Map.Entry<Character,Integer>> entryList = new ArrayList<Map.Entry<Character,Integer>>(charMap.entrySet());
		Collections.sort(entryList, 
				new Comparator<Map.Entry<Character,Integer>>() {
			public int compare(Map.Entry<Character,Integer> a, Map.Entry<Character,Integer> b) {
				return b.getValue().compareTo(a.getValue());
			}
		});
		
		System.out.println("2nd most freq: key="+entryList.get(1).getKey()+", count="+entryList.get(1).getValue());
		
		return secondChar;
	}
	
	private static void scanChar(char[] inCharArr, Map<Character, Integer> charMap) {
		for (char chLocal : inCharArr) {
			if (chLocal==' ') {
				// ignore space character
				continue;
			}
			if (!charMap.containsKey(chLocal)){
				charMap.put(chLocal, 1);
			} else {
				charMap.put(chLocal, (charMap.get(chLocal)+1));
			}
		}
	}

}

http://java.dzone.com/articles/thursday-code-puzzler-second

Calculate The Second Highest Frequency 
Write a method that accepts a String and returns the  character with the second highest frequency. For example "aabbbc" would return 'a'. If the string contains spaces, they can be disregarded from the count.

Calculate The Second Highest Frequency

java

Java