while（string.length> = 0）給出StringIndexOutOfBoundsException錯誤

Question

我有一個程序，其中我在計算字符串中的單詞數。 問題是，我需要while循環才能運行一定次數。 每次運行時，我都會創建一個切斷第一個單詞的子字符串。

程序：

public class WordCount {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        String sentence = "My name is Brad";
        int pos;
        String word;
        String newSent;
        int wordCount = 0;

        while(sentence.length() >= 0){
            pos = sentence.indexOf(' ');
            word = sentence.substring(0,pos);
            newSent = sentence.substring(pos+1);
            sentence = newSent;

            wordCount++;

            System.out.println("word = " + word);
            System.out.println("newSent = " + newSent);
            System.out.println("wordCount = " + wordCount);
        }
    }

問題是永遠不會算出最后一個字，因為那是錯誤發生的時間。

輸出：

word = My
newSent = name is Brad
wordCount = 1
word = name
newSent = is Brad
wordCount = 2
word = is
newSent = Brad
wordCount = 3
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.String.substring(Unknown Source)
    at assignment3.WordCount.main(WordCount.java:18)

更新

pos = sentence.indexOf(' ');
word = sentence.substring(0,pos);
newSent = sentence.substring(pos+1);
sentence = newSent;
if (sentence.indexOf(' ') == -1){
    newSent = "";
    word = sentence;
}
if (word.length() >= minLength){
    wordCount++;
}

編輯2：我的解決方案是有人很好奇

public static void main(String[] args) {
        // TODO Auto-generated method stub
        String sentence = "My name is Brad";
        int pos;
        String word;
        String newSent;
        int minLength = 0;
        int wordCount = 0;

        // sentence.indexOf(' ') != -1

        while(sentence.length() > 0){

            if (sentence.indexOf(' ') == -1){
                pos = sentence.length();
                newSent = "";
            } else {
                pos = sentence.indexOf(' ');
                newSent = sentence.substring(pos+1);
            }
            word = sentence.substring(0,pos);

            sentence = newSent;

            if (word.length() >= minLength){
                wordCount++;
            }


            System.out.println("word = " + word);
            System.out.println("newSent = " + newSent);
            System.out.println("wordCount = " + wordCount);
        }
    }

Answer 1

如果沒有更多空間可查，您無需檢查indexOf()的結果。

 pos = sentence.indexOf(' ');
 word = sentence.substring(0,pos);

當在其余字符串中找不到更多空間時，對indexOf()的調用將返回-1。

然后，隨后對substring(0,-1)調用將引發IndexOutOfBoundsException，因為0> -1。

從javadoc中獲取String.substring（int，int） ：

拋出： IndexOutOfBoundsException-如果beginIndex為負，或者endIndex大於此String對象的長度， 或者beginIndex大於endIndex 。