How to Split Strings with Delimiters Using Lookahead and Lookbehind?

Splitting Strings with Delimiters Using Lookahead and Lookbehind

A common task in programming is splitting a string based on specific delimiters. However, the default String.split() method only provides the split text, excluding the delimiters. In scenarios where retaining the delimiters is crucial, alternative approaches are necessary.

Lookahead and lookbehind are features of regular expressions that enable identifying patterns without actually matching them. Leveraging these features, we can split a string while preserving the delimiters.

Regex Approach:

<code class="java">String sentence = "(Text1)(DelimiterA)(Text2)(DelimiterC)(Text3)(DelimiterB)(Text4)";
String[] splitResult = sentence.split("((?=;)|(?<=;))");</code>

Interpretation:

This regex includes:

• (?=;): Positive lookahead to match an empty string before a semicolon (;).
• (?<=;): Positive lookbehind to match an empty string after a semicolon (;).
• ((?=;)|(?<=;)): Combines the lookahead and lookbehind, ensuring that either a semicolon exists before or after the split point.

By using this regex, the splitResult will contain the following elements:

[Text1, ;, Text2, ;, Text3, ;, Text4]

Conclusion:

Lookahead and lookbehind allow for advanced string manipulation by enabling the identification of patterns without directly matching them. This approach provides a versatile way to split strings based on delimiters while maintaining their original structure.

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