Java String's split method ignores empty substrings

Question

It occured to me today the behavior of java String.split() is very strange.

Actually I want to split a string "aa,bb,cc,dd,,,ee" to array by .split(",") that gives me a String array ["aa","bb","cc","dd","","","ee"] of length 7.

But when I try to split a String "aa,bb,cc,dd,,,," to array this gives me a array of length 4 means only ["aa","bb","cc","dd"] rejecting all next blank Strings.

I want a procedure that splits a String like "aa,bb,cc,dd,,,," to array ["aa","bb","cc","dd","","",""].

Is this possible with java.lang.String api? Thanks in advance.

Solution 1

Use String.split(String regex, int limit) with negative limit (e.g. -1).

"aa,bb,cc,dd,,,,".split(",", -1)

When String.split(String regex) is called, it is called with limit = 0, which will remove all trailing empty strings in the array (in most cases, see below).

The actual behavior of String.split(String regex) is quite confusing:

• Splitting an empty string will result in an array of length 1. Empty string split will always result in length 1 array containing the empty string.
• Splitting ";" or ";;;" with regex being ";" will result in an empty array. Non-empty string split will result in all trailing empty strings in the array removed.

The behavior above can be observed from at least Java 5 to Java 8.

There was an attempt to change the behavior to return an empty array when splitting an empty string in JDK-6559590. However, it was soon reverted in JDK-8028321 when it causes regression in various places. The change never makes it into the initial Java 8 release.

Solution 2

You can use public String[] split(String regex, int limit):

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. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. 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.

---

String st = "aa,bb,cc,dd,,,,";
System.out.println(Arrays.deepToString(st.split(",",-1)));
                                                    ↑

Prints:

[aa, bb, cc, dd, , , , ]

Comments

[AlexC]

This is not working for me: java -version openjdk version "1.8.0_131" OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.16.04.3-b11)

[Andy Hayden]

This is wild...!