String.split处理空格和制表符的奇怪行为

Question

I have a string consisting of tabs and spaces and some arbitrary characters. The string below is made up of space space tab tab 1 space tab -2 tab space + space .

import java.util.Arrays;

String[] s = "          1   -2   + ".split("[\\s]+");
System.out.println(Arrays.toString(s));

Running split with regex [\\s+] one would expect to get [1, -2, +] , however the returned array I get on my machine (OS X, JDK1.6.0_37) is [, 1, -2, +] .

It turns out the first element is simply "blank" ( s[0].equals("") returns true ) and so it should have been matched by \\s .

What am I missing?

Answer 1

If while splitting your string, the first character of the string is amongst the delimiter, then the first element of the generated array is always an empty string .

Take it this way, your string always starts with an empty string . So, your delimiter - \\s+ will be divide " a" string(note the leading whitespace) in two parts, first before \\s+ which is empty string "" , and one after it, which is a .

So, the output you got is obvious.

It turns out the first element is simply "blank" (s[0].equals("") returns true) and so it should have been matched by \\s.

No it shouldn't have been. A space is not an empty string. There is difference between them.