项目中遇到了这样一个问题,对 String str = ",," 调用 split(",")方法,预期结果是返回一个长度为 3 的String数组,且每一个元素都为空字符串 ""。但实际结果返还的是一个空数组,长度为 0 。
百度之,原来java中还有 split(String regex, int limit)这中用法,String[] java.lang.String.split(String regex, int limit),其中regex为分割正则表达式,limit为分割次数限制,官方文档这样解释:
1. The limit
parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n, and the array's last entry will contain all input beyond the last matched delimiter.
当 limit > 0的时候,str将被分割 limit - 1次:
1 String str = ",,,,"; 2 String [] strLst = str.split(",", 2); 3 System.out.println(strLst.length); 4 5 for (String e : strLst) { 6 System.out.println(e); 7 }
输出为:
2
,,,
2. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length.
当 limit < 0 的时候,str将被尽可能多的分割:
1 2 String str = ",,,,"; 3 String [] strLst = str.split(",", -1); 4 System.out.println(strLst.length); 5 6 for (String e : strLst) { 7 System.out.println(e); 8 }
输出为:
5
3. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded
当 limt = 0 的时候,str被尽可能多的分割,但是尾部的空字符串会被抛弃:
1 String str = ",,,,"; 2 String [] strLst = str.split(",", 0); 3 System.out.println(strLst.length); 4 for (String e : strLst) { 5 System.out.println(e); 6 } 7 8 str = "a,b,,,"; 9 strLst = str.split(",", 0); 10 System.out.println(strLst.length); 11 for (String e : strLst) { 12 System.out.println(e); 13 }
输出为:
0
2
a
b
对于 没有 limit 参数的 split函数, 官方解释如下:
This method works as if by invoking the two-argument split
method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.
也就是等价于 limt = 0 的情况,尾部的空字符串被舍弃掉:
1 String str = "a,b,,,"; 2 String [] strLst = str.split(","); 3 System.out.println(strLst.length); 4 for (String e : strLst) { 5 System.out.println(e); 6 }
输出为:
2
a
b