HashMap<Character,Integer> map = new HashMap<Character,Integer>();
String s = "aasjjikkk";
for(int i = 0; i < s.length(); i++){
   char c = s.charAt(i);
   Integer val = map.get(new Character(c));
   if(val != null){
     map.put(c, new Integer(val + 1));
   }else{
     map.put(c,1);
   }
}

Multiset<Character> chars = HashMultiset.create();
for (int i = 0; i < string.length(); i++) {
    chars.add(string.charat(i));
}

public class Pair
{
    private char letter;
    private int count;
    public Pair(char letter, int count)
    {
        this.letter = letter;
        this.count= count;
    }
    public char getLetter(){return key;}
    public int getCount(){return count;}
}

public static Pair countCharFreq(String s)
{
    String temp = s;
    java.util.List<Pair> list = new java.util.ArrayList<Pair>();
    while(temp.length() != 0)
    {
        list.add(new Pair(temp.charAt(0), countOccurrences(temp, temp.charAt(0))));
        temp.replaceAll("[" + temp.charAt(0) +"]","");
    }
}

public static int countOccurrences(String s, char c)
{
    int count = 0;
    for(int i = 0; i < s.length(); i++)
    {
        if(s.charAt(i) == c) count++;
    }
    return count;
}

Hashtable<Character,Integer> table = new Hashtable<Character,Integer>();
String str = "aasjjikkk";
for( c in str ) {
    if( table.get(c) == null )
        table.put(c,1);
    else
        table.put(c,table.get(c) + 1);
}

for( elem in table ) {
    println "elem:" + elem;
}