Regex for string splitting not working properly

Question

I want to split a string in 2 characters without any delimiter, but Regex split is not working properly

here is my code:-

  String str="splitstring";
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})").length);
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})")[0]);
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})")[1]);

output:-

 Split..2

 Split..sp

 Split..litstring

Answer 1

Looks like it's a bug with the result threshold limit in your Java environment. Try to workaround it by providing the limit explicitly:

    String str="splitstring";
    int partsCount = (str.length() + 1) / 2;
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})", partsCount).length);
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})", partsCount)[0]);
    System.out.println("Split.."+str.trim().split("(?<=\\G.{2})", partsCount)[1]);

Answer 2

我假设你想把字符串分成两个相等的一半，子串..那么这可能会有所帮助!!

System.out.println("Split.."+str.trim().split("(?=\\D)")[0]);

Answer 3

Why do you use a regex for this?

You can do something like this:

String str = "splitstring";
System.out.println("String-length: " + str.length());
for (int i = 0; i < str.length(); i += 2) { // Increments of 2
  System.out.print("Split.." + str.charAt(i));
  if (i != str.length() - 1) {
    System.out.print(str.charAt(i + 1));
  }
  System.out.println();
}

Output:

String-length: 11
Split..sp
Split..li
Split..ts
Split..tr
Split..in
Split..g

---

EDIT: If you insist of using the regex though, here it is:

final String str = "splitstring";
System.out.println(Arrays.toString(
    str.split("(?<=\\G.{2})")
));

Output remains the same as above. Seems like there is indeed a bug or something, since the regex is the same as in your question.. Can't really say for sure though, since it's not really my expertise.

---

EDIT 2: Jon Skeet has an alternative method that is more efficient than mine above :

Well, it's fairly easy to do this by brute force:

 public static List<String> splitEqually(String text, int size) { // Give the list the right capacity to start with. You could use an array // instead if you wanted. List<String> ret = new ArrayList<String>((text.length() + size - 1) / size); for (int start = 0; start < text.length(); start += size) { ret.add(text.substring(start, Math.min(text.length(), start + size))); } return ret; } 

I don't think it's really worth using a regex for this.

EDIT: My reasoning for not using a regex:

• This doesn't use any of the real pattern matching of regexes. It's just counting.
• I suspect the above will be more efficient, although in most cases it won't matter
• If you need to use variable sizes in different places, you've either got repetition or a helper function to build the regex itself based on a parameter - ick.
• The regex provided in another answer firstly didn't compile (invalid escaping), and then didn't work. My code worked first time. That's more a testament to the usability of regexes vs plain code, IMO.