当索引1中没有元素时，为什么不跟随java代码抛出java.lang.StringIndexOutOfBoundsException？

String str="x"; System.out.println(str.substring(1)); 

来自Javadoc：

String java.lang.String.substring(int beginIndex) ：返回一个新字符串，它是该字符串的子字符串。 子字符串以指定索引处的字符开头，并延伸到此字符串的末尾。

Answer 1

看看JavaDoc ，并特别注意“空虚”的例子：

 Returns a 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. Examples: "unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string) Parameters: beginIndex the beginning index, inclusive. Returns: the specified substring. Throws: IndexOutOfBoundsException - if beginIndex is negative or larger than the length of this String object 

if beginIndex is negative or larger than the length of this String object则抛出exception; 在您的情况下，beginIndex等于字符串的长度，而不是更大。