java - 字符串索引越界异常 : string index out of range

Question

我找不到有关此异常的答案。程序很简单，但是我不知道为什么不正确。

/**
 * Program selects the first word from the sentence "Hello, my dear!" with
 * the String Classes's methods this.indexOf() and this.substring()  
 * 
 *
 * Last modify: 29th October 2015
 */

public class TakeSubstringWanted {

    public static void main(String[] args) {

        String sentence = "Hello, my dear!";
        String reference = "Hello";

        System.out.println("The sentence is: " + sentence);
        System.out.println("You want to take the first word of that sentence");
        System.out.println("Give me a second...");

        int firstReference = sentence.indexOf(reference);
        int firstLength = reference.length();
        System.out.println("The first reference of the searched word is " + firstReference);
        System.out.println("The first word of the sentence " + sentence + " is: " + "\"" + sentence.substring(firstReference, firstLength) + "\"");
        int secondReference = sentence.indexOf("my");
        System.out.println("The second reference of the searched word is " + secondReference);
        int secondLength = "my".length();
        System.out.println(secondLength);
        System.out.println(sentence);
        System.out.println("The second word of the sentence " + sentence + " is: " + "\"" + sentence.substring(secondReference, secondLength) + "\"");
    }

}

Answer 1

你的问题在最后一行:

System.out.println("The second word of the sentence " + sentence + " is: "
             + "\"" + sentence.substring(secondReference, secondLength) + "\"");

因为您的 secondReference = 7 和 secondLength = 2，但是如果您查看 documentation对于子字符串方法:

public String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

...

Throws: IndexOutOfBoundsException - if beginIndex or endIndex are negative, if endIndex is greater than length(), or if beginIndex is greater than startIndex

意思是，您要求 substring 返回从索引 7 到索引 2 的字符串，这会导致 IndexOutOfBoundsException。您可能想要做的是:

sentence.substring(secondReference, secondReference + secondLength)