字符串子字符串索引可以是字符串的长度 [英] String substring index could be the length of string

问题描述

这是Java字符串问题.我使用substring(beginindex)来获取子字符串. 考虑到String s="hello"，该字符串的长度为5.但是，当我使用s.substring(5)或s.substring(5,5)时，编译器没有给我错误.字符串的索引应从0开始长度为1. 为什么不适用于我的情况?我认为s.substring(5)应该给我一个错误，但是没有.

This is a Java string problem. I use the substring(beginindex) to obtain a substring. Considering String s="hello", the length of this string is 5. However when I use s.substring(5) or s.substring(5,5) the compiler didn't give me an error. The index of the string should be from 0 to length-1. Why it doesn't apply to my case? I think that s.substring(5) should give me an error but it doesn't.

推荐答案

因为endIndex是排他的，如

IndexOutOfBoundsException-如果beginIndex为负或endIndex 大于此String对象的长度，或者beginIndex为 大于endIndex.

IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

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我认为当我使用s.substring(5)时，它应该给我错误 没有

I think when I use s.substring(5), it should give me error while it didn't

为什么会这样?

返回一个新字符串，该字符串是该字符串的子字符串.子串 以指定索引处的字符开头，并扩展到 该字符串的结尾.

Returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

由于beginIndex不大于endIndex(在您的情况下为5)，因此完全有效.您只会得到一个空字符串.

Since the beginIndex is not larger than the endIndex (5 in your case), it's perfectly valid. You will just get an empty String.

如果您查看源代码:

1915  public String substring(int beginIndex) {
1916      return substring(beginIndex, count);
1917  }
....
1941  public String substring(int beginIndex, int endIndex) {
1942      if (beginIndex < 0) {
1943          throw new StringIndexOutOfBoundsException(beginIndex);
1944      }
1945      if (endIndex > count) {
1946          throw new StringIndexOutOfBoundsException(endIndex);
1947      }
1948      if (beginIndex > endIndex) {
1949          throw new StringIndexOutOfBoundsException(endIndex - beginIndex);
1950      }
1951      return ((beginIndex == 0) && (endIndex == count)) ? this :
1952          new String(offset + beginIndex, endIndex - beginIndex, value);
1953  }

因此s.substring(5);等同于s.substring(5, s.length());，在您的情况下为s.substring(5,5);.

Thus s.substring(5); is equivalent to s.substring(5, s.length()); which is s.substring(5,5); in your case.

当您调用s.substring(5,5);时，由于您正在调用count值为0的构造函数(这是私有程序包)，因此它会返回一个空字符串(count表示字符串中的字符数) ):

When you're calling s.substring(5,5);, it returns an empty String since you're calling the constructor(which is private package) with a count value of 0 (count represents the number of characters in the String):

644 String(int offset, int count, char value[]) {
645         this.value = value;
646         this.offset = offset;
647         this.count = count;
648 }

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