我正在尝试学习Java并进行了一项练习，该练习是获取字符串中的第一个唯一项。 我使用HashTable作为字符串的字符作为键，并使用计数器将其在字符串中看到多少次作为值。
After that, I'm iterating over the HashTable and checking for each key if it has a value of 1 (only seen once) I want to return it.
The problem is, when I have a string like this for example abcdcd a and b are both unique, but a is the first one, but for some reason, when I get the keys on the HashTable, the b comes before a.
这就是我所拥有的：
public static Character firstNonRepeatedCharacter(String str) {
Hashtable<Character, Integer> characters = new Hashtable<Character, Integer>();
char[] charsInString = str.toCharArray();
for(int i=0; i<charsInString.length; i++){
if (characters.containsKey(charsInString[i])){
int counter = characters.get(charsInString[i]);
counter ++;
characters.put(charsInString[i], counter);
}else {
characters.put(charsInString[i], 1);
}
}
Enumeration<Character> enumeration = characters.keys();
while(enumeration.hasMoreElements()) {
Character key = enumeration.nextElement();
if(characters.get(key) == 1) {
return key;
}
}
return null;
}
为什么会这样呢？
