关于String.substring方法

最新推荐文章于 2024-10-29 16:20:17 发布

最新推荐文章于 2024-10-29 16:20:17 发布 · 189 阅读

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本文详细解析了Java中String类的subString方法的工作原理及其使用案例，包括单参数和双参数版本的方法签名，并列举了可能遇到的各种边界情况。

关于String.substring方法

该方法的签名为

String substring(int beginIndex, int endIndex)

结合javadoc和源代码，对该方法进行分析：

根据beginIndex与0或count的比较、beginIndex与endIndex的比较、endIndex与字符串长度count的比较，有几种情况：

#	beginIndex与0比较	beginIndex与endIndex比较	endIndex与count比较	结果
1	<0			IndexOutOfBoundsException
2	=0	<	<	子串
3		<	=	String对象本身
4		<	>	IndexOutOfBoundsException
5		=		"" 空串
6		>		IndexOutOfBoundsException
7	>0 & <count	<	<	子串
8		<	=	子串
9		<	>	IndexOutOfBoundsException
10		=		"" 空串
11		>		IndexOutOfBoundsException
12	=count	<		IndexOutOfBoundsException
13		=		"" 空串
14		>		IndexOutOfBoundsException
15	>count			IndexOutOfBoundsException

上面的表格列出的情况多达15种，可见要对代码进行覆盖性测试确实是非常困难的。

jdk6中String.substring的文档写道

public String substring(int beginIndex)

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.

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.

public String substring(int beginIndex,
                        int endIndex)

Returns a new 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.

Examples:

 "hamburger".substring(4, 8) returns "urge"
 "smiles".substring(1, 5) returns "mile"

Parameters:

beginIndex - the beginning index, inclusive.

endIndex - the ending index, exclusive.

Returns:

the specified substring.

Throws:

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

PS：iteye的表格编辑实在很困难，望高人指点。