Isomorphic Strings

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        //http://blog.csdn.net/fightforyourdream/article/details/17311575
        if(s.length()!=t.length()) return false;
        HashMap<Character, Character> hm1 = new HashMap<Character, Character>();
        HashMap<Character, Character> hm2 = new HashMap<Character, Character>();
        for(int i=0;i<s.length();i++){
            char c1 = s.charAt(i);
            char c2 = t.charAt(i);
            if(hm1.containsKey(c1)){
                if(hm1.get(c1)!=c2)
                    return false;
            }
            if(hm2.containsKey(c2)){
                if(hm2.get(c2)!=c1)
                    return false;
            }
            hm1.put(c1,c2);
            hm2.put(c2,c1);
        }
        return true;
    }
}