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Thread: "?" replacement

  1. #1
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    Default "?" replacement

    I'm making the encryption program mentioned in my other post. When I type all other character besides " ' /\ and . it works fine besides the question mark. It gives me this error when ever i type in a question mark:

    Options:
    ---------------
    |1. Encryption|
    |2. Decryption|
    ---------------

    Enter your choice:
    1

    Enter the phrase you want encrypted:
    ?
    Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta
    character '?' near index 0
    ?
    ^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.sequence(Unknown Source)
    at java.util.regex.Pattern.expr(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.util.regex.Pattern.<init>(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.lang.String.replaceAll(Unknown Source)
    at encryption.main(encryption.java:376)
    Press any key to continue . . .
    This is the code for replacing the ?:
    			if (pdphrase.contains("?")) {
     
    				pdphrase = pdphrase.replaceAll("?", "24");
     
    			}

    I don't know whats going on or if I should just scrap that character like i did others. The period caused every number to change it its number and the other ones caused errors when compiling. Please Help!
    Last edited by sp11k3t3ht3rd; January 10th, 2011 at 07:52 PM.


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: "?" replacement

    String.replace uses Java's Regex engine which uses those characters (actually, I think there are a few other characters such as *) for special behaviors.

    The simple solution is to manually search the string yourself, or to ensure that the user enters a valid Java Regex pattern. See: Lesson: Regular Expressions (The Java™ Tutorials > Essential Classes)

  3. The Following 2 Users Say Thank You to helloworld922 For This Useful Post:

    javapenguin (March 26th, 2011), sp11k3t3ht3rd (January 10th, 2011)

  4. #3
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    Default Re: "?" replacement

    Alright thanks! I might just take out the characters that are used in the Java Regex engine. This is only for my sophomore level science fair so it won't matter and I dont want peoples heads exploding when I try to explain it to them in my presentation...

  5. #4
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    Default Re: "?" replacement

    "?" is special to regular expression. try escaping it. "\\?"

  6. The Following User Says Thank You to JavaHater For This Useful Post:

    javapenguin (March 26th, 2011)

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