java为什么这些案例不返回IndexOutofBoundsException？

Question

我最近偶然发现了这一点。为什么以下情况不返回IndexOutofBoundsException

public static void main(String[] args) {
    String str = "String";
    System.out.print(str.substring(0, 0));
}

public static void main(String[] args) {
    String str = "String";
    System.out.print(str.substring(str.length()));
}

我一直被告知这一点。子字符串（inti，intk）返回从索引i到k-1的子字符串。在第一种情况下，子字符串不是从索引0到-1吗？为什么这不会产生越界错误？我也有同样的问题。长度（）的情况下，以及

Answer 1

从Java 8 API开始：

public String substring(int beginIndex, int endIndex)

Returns a 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 the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

是阴性吗？不，是0
endIndex是否大于字符串的长度？不，0<；6.
beginIndex比endIndex大吗？不，他们都是0

I have the same question with the .length() case as well.

你为什么期望它抛出异常length()从不扔

Answer 2

看看substring javadoc：

Returns a 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.

因此，"String".substring(0, 0)只返回空字符串""

看看length javadoc：

Returns the length of this string. The length is equal to the number of Unicode code units in the string.

因此"String".length()返回5

Answer 3

StringJavaDoc表示IndexOutOfBoundsException将被抛出，如果：

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

您的示例不符合任何这些标准，因此不会引发异常。如果开始索引和结束索引相等，结果总是得到一个空的String

对于第二个例子，我不太确定你的问题是什么.length()只返回String包含的字符数。在上面的示例中，它只返回int6