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Thread: Question to Pattern.matches and escape sequences

  1. #1
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    Default Question to Pattern.matches and escape sequences

    I have a question regarding regular expressions and the Pattern.matches function. Right now I'm experimenting around a bit and found a strange behaviour I can't explain. Maybe some of you can.
    Let's say we have:
    String s= "abc\nabc";
    System.out.println(Pattern.matches("abc\nabc", s));
    System.out.println(Pattern.matches("abc\\nabc", s));
    System.out.println(Pattern.matches("abc\\\nabc", s));
    Why do all three matches yield true?
    For the second one it's clear, since \n is a regex-expression and the first backslash quotes it. But the rest is not so clear, especially the third one. Can someone explain it to me?

  2. #2
    Member snowguy13's Avatar
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    Default Re: Question to Pattern.matches and escape sequences

    The first one matches because the two strings are exactly the same. The "\n" in both strings represents a new line.

    In the second one, "\\" is read as a single "\" in an input string. This may match because the "n" following is then treated literally and NOT as a new line.

    The third one is weird... The first "\\" would be read as a "\" in the input string, so I don't know how there's something to match the new line...

    "abc\\\nabc" represents this string:


    The input string could be either

    abc" (as the first matcher finds)


    "abc\nabc" (as the second matcher finds)

    So I honestly don't know what's going on with that third one. To learn more about regular expressions, check out Oracle's tutorial. It's quite enlightening.
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  3. #3
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    Default Re: Question to Pattern.matches and escape sequences

    Ok, thank you. I thought that this is something obvious and I'm just to blind to see it

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