String＃split方法混淆

Question

I tried this code:

String str =",,,,,";
String str2=",,,,, ";
System.out.println(str.split(",").length);
System.out.println(str2.split(",").length);

And the output is:

0
6

The only difference is str value is ,,,,, ( without space ) and str2 value is ,,,,, ( with space )

Anybody can explain this?

Answer 1

Because in String#split() method, trailing empty String will not included in the array result.

String str =",,,,,";
String str2=",,,,, ";

As str.split(",") will supposed to give you [, , , , ,] , It return [] instead, because you have a trailing empty String there.

Different from str2.split(",") it will give you

[, , , , , ]
          ^ //note the whitespace element 

You may try

System.out.println(",,,,, ,,,,".split(",").length);

This will still give you the output: 6 , which is [, , , , , ] because after the whitespace , all you have is trailing empty string (therefore not included in the array result)

---

Note: You can keep the trailing empty strings by specifying the limit:

System.out.println(str.split(",", -1).length);
                                   ^ limit

Output : 6

Check the String#split Documentation for more details

Answer 2

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. taken from the String documentation.

Had your second string been ",,, ,," then the length would have been 4.

Hope that explains it clearly.