Question

我正在编写一个程序来反转句子中的单词顺序。（例如“红帽属于约翰”=＆gt;“约翰属于帽子红色”）我自己走过了do-while循环，但我不明白为什么会有一个索引异常。

感谢您的帮助，

JonBrown

例外：

   Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -23
    at java.lang.String.substring(Unknown Source)
    at WordReverse.main(WordReverse.java:17)

代码：

   public class WordReverse 
    {
        public static void main(String[] args)
        {
            String input = "The red had belongs to John";
            String reverse = "";
            int lastSpace = 0;

            do
            {
            //Isolate Word w/ Preceding Space
            int startIndex = lastSpace;
            int endIndex = input.indexOf(' ', startIndex + 1);

            //Add Word to front of String 
            reverse = input.substring(startIndex, endIndex) + reverse;

            //Add Preceding Space for First Iteration
            if (lastSpace == 0) reverse = " " + reverse;

            //Reset Last Space
            lastSpace = endIndex;

            // Repeat Loop Until line14 .indexOf returns -1 due to lack of " ". 
            }while (lastSpace != -1);

            System.out.println(reverse);
        }
    }

Answer 1

来自MSDN String.Substring Method (Int32, Int32)

public string Substring(
    int startIndex,
    int length
)

它应该是这样的：

reverse += input.substring(startIndex, endIndex - startIndex);

Answer 2

为方便起见，只需使用拆分

    String input = "The red had belongs to John";

    String arr[] = input.split(" ");

    for (int x = arr.length -1; x >= 0; x--) 
         System.out.println(arr[x]);

Answer 3

这个解决方案更优雅：

public class WordReverse 
{
    public static void main(String[] args)
    {
        String input = "The red had belongs to John";
        String array = input.split(" ");
        for( int i = array.length()-1; i >= 0; i++ )
          System.out.print( array[ i ] + " " );
        System.out.println();
    }
}

Answer 4

当您到达最后一个空格（“John”之前）时，endIndex值为-1。然后，您尝试使用小于subString()的{{1}}来调用endIndex，这会导致崩溃。

Answer 5

正如其他人所说，你的问题是lastIndex为-1。当发生这种情况时，此修复程序会中断循环，但在将字符串的其余部分复制到结果之前不会：

public class WordReverse 
{
    public static void main(String[] args)
    {
        String input = "The red hat belongs to John";
        String reverse = "";
        int lastSpace = 0;

        do
        {
            //Isolate Word w/ Preceding Space
            int startIndex = lastSpace;
            int endIndex = input.indexOf(' ', startIndex+1);
            if (endIndex==-1) {
                reverse = input.substring(startIndex) + reverse;
                break;
            }

            //Add Word to front of String 
            reverse = input.substring(startIndex, endIndex) + reverse;

            //Add Preceding Space for First Iteration
            if (lastSpace == 0) reverse = " " + reverse;

            //Reset Last Space
            lastSpace = endIndex;

            // Repeat Loop Until line14 .indexOf returns -1 due to lack of " ". 
        }while (true);

        System.out.println(reverse);
    }
}

StringIndexOutOfBoundsException：String.substring（）和String.indexOf（）的问题

5 个答案: