Checking if two strings are permutations of each other

Question

How to determine if two strings are permutations of each other

Answer 1

public boolean isPermutationOfOther(String str, String other){
    if(str == null || other == null)
        return false;
    if(str.length() != other.length())
        return false;

    Map characterCount = new HashMap();
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        int count = 1;
        if(characterCount.containsKey(c)){
            int k = characterCount.get(c);
            count = count+k;
        }

        characterCount.put(c, count);

    }

    for (int i = 0; i < other.length(); i++) {
        char c = other.charAt(i);
        if(!characterCount.containsKey(c)){
            return false;
        }

        int count = characterCount.get(c);
        if(count == 1){
            characterCount.remove(c);
        }else{
            characterCount.put(c, --count);
        }
    }

    return characterCount.isEmpty();
}