为何“超出范围”没有为'substring（startIndex，endIndex）'抛出 [英] Why is "out of range" not thrown for 'substring(startIndex, endIndex)'

问题描述

在Java中我使用的是 substring（）方法，我不确定为什么它没有抛出out of index错误。

In Java I am using the substring() method and I'm not sure why it is not throwing an "out of index" error.

字符串 abcde 索引从0开始到4，但 substring（）方法将startIndex和endIndex作为参数，基于我可以调用foo.substring（0）并获取abcde这一事实。

The string abcde has index start from 0 to 4, but the substring() method takes startIndex and endIndex as arguments based on the fact that I can call foo.substring(0) and get "abcde".

那么为什么子串（5）工作？该指数应该超出范围。解释是什么？

Then why does substring(5) work? That index should be out of range. What is the explanation?

/*
1234
abcde
*/
String foo = "abcde";
System.out.println(foo.substring(0));
System.out.println(foo.substring(1));
System.out.println(foo.substring(2));
System.out.println(foo.substring(3));
System.out.println(foo.substring(4));
System.out.println(foo.substring(5));

此代码输出：

abcde
bcde
cde
de
e
     //foo.substring(5) output nothing here, isn't this out of range?

当我用6替换5时：

foo.substring(6)

然后我收到错误：

Exception in thread "main" java.lang.StringIndexOutOfBoundsException:
    String index out of range: -1

推荐答案

根据 Java API doc ，substring在启动索引时抛出错误大于字符串的 Length 。

According to the Java API doc, substring throws an error when the start index is greater than the Length of the String.

IndexOutOfBoundsException - 如果
beginIndex为负数或更大比
这个String对象的长度。

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

事实上，他们举了一个像你的例子：

In fact, they give an example much like yours:

"emptiness".substring(9) returns "" (an empty string)

我想这意味着最好考虑一个Java String如下所示，其中索引包含在 | 中：

I guess this means it is best to think of a Java String as the following, where an index is wrapped in |:

|0| A |1| B |2| C |3| D |4| E |5|

这就是说字符串同时包含起始和结束索引。

Which is to say a string has both a start and end index.

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