0157. Unique Characters

public class Solution {
    /*
     * @param str: A string
     * @return: a boolean
     */
    public boolean isUnique(String str) {
        boolean[] occur = new boolean[146];
        for(int i = 0; i<str.length(); i++){
            if(occur[str.charAt(i)-32]){
                return false;
            }
            else{
                occur[str.charAt(i)-32] = true;
            }
        }
        return true;
    }
}