String#contains using Pattern

Maarten Bodewes :

If I would want to make a 100% clone of String#contains(CharSequence s): boolean in Java regex using Pattern. Would the following calls be identical?

input.contains(s);

and

Pattern.compile(".*" + Pattern.quote(s) + ".*").matcher(input).matches();

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Similarly, would the following code have the same functionality?

Pattern.compile(Pattern.quote(s)).matcher(input).find();

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I presume that the regex search is less performant, but only by a constant factor. Is this correct? Is there any way to optimize the regular expressions to mimic contains?

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The reason that I'm asking is that I have a piece of code that is written around Pattern and it seems wasteful to create a separate piece of code that uses contains. On the other hand, I don't want different test results - even minor ones - for each code. Are there any Unicode related differences, for instance?

Wiktor Stribiżew :

If you need to write a .contains like method based on Pattern, you should choose the Matcher#find() version:

Pattern.compile(Pattern.quote(s)).matcher(input).find()

If you want to use .matches(), you should bear in mind that:

• .* will not match line breaks by default and you need (?s) inline modifier at the start of the pattern or use Pattern.DOTALL option
• The .* at the pattern start will cause too much backtracking and you may get a stack overflow exception, or the code execution might just freeze.