LeetCode-Word Pattern

Given a pattern and a string str, find if str follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.

Examples:
pattern = "abba", str = "dog cat cat dog" should return true.
pattern = "abba", str = "dog cat cat fish" should return false.
pattern = "aaaa", str = "dog cat cat dog" should return false.
pattern = "abba", str = "dog dog dog dog" should return false.
Notes:
You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.

public class Solution {
    public boolean wordPattern(String pattern, String str) {
        //boolean followPattern=true;
        if(pattern == null || pattern.length() == 0){
            return false;
        }
        String[] strArray=str.split(" ");
        if(strArray.length != pattern.length()){
            return false;
        }
        Map<Character, String> patternMap=new HashMap<Character, String>();
        for(int i=0; i<pattern.length(); i++){
            char c=pattern.charAt(i);
            if(patternMap.containsKey(c)){
                String value=patternMap.get(c);
                if(!value.equals(strArray[i])){
                    return false;
                }
            }
            else{
                for(Character ca : patternMap.keySet()){
                    if(patternMap.get(ca).equals(strArray[i])){
                        return false;
                    }
                }
                patternMap.put(c, strArray[i]);
            }
        }
        return true;
    }
}