Java确定字符串中的每个字符是否为字母

Question

I'm using isLetter() and charAt() to see if a character in str is a letter or not. The use of this method is to find the number of words in a string that are at least the minimum word length. I don't want it to count anything other than letters. (im a java noob)

public static int wordCount(String str, int minLength) {     
//Method that counts words.

    int count = 0;
    boolean isLetter = false;
    for (int i = 0, wordLength = 0; i < str.length() + 1; i++) {
        isLetter = Character.isLetter(str.charAt(i)); //Why doesn't this line work?
        if (i == str.length() || str.charAt(i) == ' ' || isLetter==false) { 
            if (wordLength >= minLength) {              
                count++;                                                
            }
            wordLength = 0;                                 
        } else {                                                            
            wordLength++;                                       
        }
    }
    return count;
}

Answer 1

The problem is in your for loop. You have it iterate until i < str.length() + 1 . That means at some point, you will be asking for str.charAct(str.length()) . Because Java arrays (and Strings) index from 0, the index is too high and will break.

Instead, just have your for loop iterate until i < str.length() . That should fix it.

Answer 2

It's not the Character.isLetter not working, it's the str.charAt(i) that throws an exception when i reaches str.length() .

Your loop iterates i from 0 to str.length() , inclusive - a total of str.length()+1 characters. The call of charAt(i) when i is str.length() would be illegal.

To fix this problem, remove + 1 from the expression in the for loop, or make sure that str.charAt(i) is not called when i is equal to str.length() . For example, you could use the short-circuiting feature like this:

for (int i = 0, wordLength = 0; i < str.length() + 1; i++) {
    if (i == str.length() || !Character.isLetter(str.charAt(i))) {
        ...
    }
}

Above, str.charAt(i) is not called when i == str.length() , preventing the crash ( demo ).

You may want to change a few more things:

• str.charAt(i) == ' ' || isLetter==false str.charAt(i) == ' ' || isLetter==false can be reduced to isLetter==false or even to !isLetter , because space character is not a letter
• The declaration of isLetter can be moved inside the loop, and combined with initialization (unless you decide to get rid of the variable altogether using the code snipped shown above).