StringIndexOutOfBoundsException 错误

Question

我是 JAVA 新手，我正在处理以下任务：

1. 将用户字符串作为输入
2. 将用户整数作为输入
3. 使用整数作为增量值
4. 返回字符串中从 0 开始到递增后可用的最后一个字符结束的所有字符值。

我在终端中得到了正确的结果，紧接着是可怕的 StringOutOfBoundsException 错误。我无法看到我试图访问字符串中超出范围的字符的位置，并感谢您找到我的错误的专业知识。这是我的代码的 sn-p：

import java.util.*;
public class EveryOtherCharacter
{
   public static void main(String[] args)
   {
    Scanner input = new Scanner(System.in);    

    //initialize all variables to be used in this program
    String userEntry;//store user word as a String
    String error=("Invalid Entry!");//notify of error
    String purpose=("Enter a word and an increment value and we'll\nreturn each character in your word using the number you provided".)
    int increment;//store increment integer from user
    int userEntryCount;//store total count of chars in userEntry
    char value;//get character at increment value from userEntry

    System.out.println("========================START PROGRAM=============================");
   System.out.println(purpose); 

    System.out.println();//whitespace
    System.out.print("Enter a word: ");
    userEntry=input.nextLine();
    userEntryCount = userEntry.length();

    System.out.print("Enter an increment value:  ");
    increment=input.nextInt();
    System.out.println();//whitespace

    value=userEntry.charAt(0);
    System.out.print(value);

    for (int count=0; count <= userEntryCount; count++)
    {
        value=userEntry.charAt(increment);
        userEntry=userEntry.substring(increment);
        System.out.print(value);
    }

    if (increment > userEntryCount && increment <= 0)
    {
        System.out.println(error);
    }
     System.out.println();//whitespace

    System.out.println("=========================END PROGRAM==============================");

   }
}

这是运行此程序后我的终端输出的示例。请注意，正确的输出出现在异常错误之前：

java EveryOtherCharacter
========================START PROGRAM=============================
Enter a word and an increment value and we'll
return each character in your word using the number you provided

Enter a word: whyisthissohard
Enter an increment value:  3

wihsaException in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 3
at java.lang.String.charAt(String.java:658)
at EveryOtherCharacter.main(EveryOtherCharacter.java:57)

Answer 1

我最终使用 while 循环解决了这个问题，如下所示：

while (n < length)//where n=userNumber & length=length of user word
{
    character=userEntry.charAt(n);//character becomes the character of the word at the increment value
    System.out.print(character);//print value of character at increment
    userEntry=userEntry.substring(n);//set userEntry to value of new string starting at n
    length = userEntry.length();//count the total number of characters in the new substring
}

在经历了 for 循环的逻辑之后，我意识到我已经创建并试图增加 i 的值，而这并不是必需的。你们都对解决问题提供了很大的帮助。感谢您的帮助！

Answer 2

我认为当说明说“使用整数作为增量值”时，您应该像这样将其用作实际增量值。

public static void main(String[] args) {

    String s = "whyisthissohard";
    int skip = 3;

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < s.length(); i += skip) { // <--- Increment value
        sb.append(s.charAt(i));
    }

    //Return all character values in the string
    System.out.println(sb.toString()); // wihsa

}

如果需要，您也可以在 for 循环中将它们全部打印出来，而不是添加到另一个字符串中。

Answer 3

您每次通过 whyisthissohard 减少 3 个。但是您总共循环了whyisthissohard 的长度。

for (int count=0; count <= userEntryCount; count++)
{
    value=userEntry.charAt(increment);
    userEntry=userEntry.substring(increment);
    System.out.print(value);
}

---

First loop : value = 'i' ; userEntry = "isthissohard" ;
Second loop : value = 'h' ; userEntry = "hissohard";
Third loop : value = 's' ; userEntry = "sohard";
Fourth loop : value = 'a' ; userEntry = "ard";
Fifth loop => Error