Question

I want to using regex on Java to split a number string.
I using a online regex tester test the regex is right.
But in Java is wrong.

Pattern pattern = Pattern.compile("[\\\\d]{1,4}");
String[] results = pattern.split("123456");
// I expect 2 results ["1234","56"]
// Actual results is ["123456"]

Anything do I missing?

---

I knows this question is boring. But I wanna to solve this problem.
Answer

Pattern pattern = Pattern.compile("[\\d]{1,4}");
String[] results = pattern.split("123456");
// Results length is 0
System.out.println(results.length);

is not working. I have try it. It’s will return nothing on the results.
Please try before answer it.

Sincerely thank the people who helped me.

---

Solution:

Pattern pattern = Pattern.compile("([\\d]{1,4})");
Matcher matcher = pattern.matcher("123456");
List<String> results = new ArrayList<String>();
while (matcher.find()) {
    results.add(matcher.group(1));
}

Output 2 results [“1234″,”56”]

Answer 1

Pattern pattern = Pattern.compile("[\\\\d]{1,4}")

Too many backslashes, try [\\d]{1,4} (you only have to escape them once, so the backslash in front of the d becomes \\. The pattern you wrote is actually [\\d]{1,4} (a literal backslash or a literal d, one to four times).

When Java decided to add regular expressions to the standard library, they should have also added a regular expression literal syntax instead of shoe-horning it over Strings (with the unreadable extra escaping and no compile-time syntax checking).