How to split a string, but also keep the delimiters?

by

You can use lookahead and lookbehind, which are features of regular expressions.

System.out.println(Arrays.toString("a;b;c;d".split("(?<=;)")));
System.out.println(Arrays.toString("a;b;c;d".split("(?=;)")));
System.out.println(Arrays.toString("a;b;c;d".split("((?<=;)|(?=;))")));

And you will get:

[a;, b;, c;, d]
[a, ;b, ;c, ;d]
[a, ;, b, ;, c, ;, d]

The last one is what you want.

((?<=;)|(?=;)) equals to select an empty character before ; or after ;.

EDIT: Fabian Steeg’s comments on readability is valid. Readability is always a problem with regular expressions. One thing I do to make regular expressions more readable is to create a variable, the name of which represents what the regular expression does. You can even put placeholders (e.g. %1$s) and use Java’s String.format to replace the placeholders with the actual string you need to use; for example:

static public final String WITH_DELIMITER = "((?<=%1$s)|(?=%1$s))";

public void someMethod() {
    final String[] aEach = "a;b;c;d".split(String.format(WITH_DELIMITER, ";"));
    ...
}

More Related Contents:

  1. What do the characters ((?:(?:(?: mean in pattern-matching? [duplicate]
  2. Java: splitting a comma-separated string but ignoring commas in quotes
  3. Use String.split() with multiple delimiters
  4. Java how to replace 2 or more spaces with single space in string and delete leading and trailing spaces
  5. Java Regex Capturing Groups
  6. What is the regex to extract all the emojis from a string?
  7. How to remove special characters from a string?
  8. Splitting string with pipe character (“|”) [duplicate]
  9. RegEx to split camelCase or TitleCase (advanced)
  10. Compare one String with multiple values in one expression
  11. Replace the last part of a string
  12. Java equivalent to PHP’s preg_replace_callback
  13. java.lang.StackOverflowError while using a RegEx to Parse big strings
  14. Split regex to extract Strings of contiguous characters
  15. Java regex – overlapping matches
  16. Generic support for ISO 8601 format in Java 6
  17. Find everything between two XML tags with RegEx
  18. Parsing CSV input with a RegEx in java
  19. simple java regex throwing illegalstateexception [duplicate]
  20. Range of valid character for a base 64 encoding
  21. Regex: ?: notation (Question mark and colon notation) [duplicate]
  22. Whats the difference between \z and \Z in a regular expression and when and how do I use it?
  23. Regex reuse a pattern to capture multiple groups?
  24. Java Regex pattern that matches in any online tester but doesn’t in Eclipse
  25. Java Pattern Matcher: create new or reset?
  26. How can split a string which contains only delimiter?
  27. Regular expression to get an attribute from HTML tag
  28. Issue with Java Regex \b
  29. Java’s Scanner vs String.split() vs StringTokenizer; which should I use?
  30. java regex pattern unclosed character class

Leave a Comment