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  1. import java.util.*;
  2. import java.util.regex.*;
  3.  
  4. class Ideone
  5. {
  6. 	public static String username(String str) {
  7. 	    return Boolean.toString( str.trim().matches("[a-zA-Z]\\w{3,24}$(?<!_)") );
  8. 	}
  9. 	public static void main (String[] args) throws java.lang.Exception
  10. 	{
  11. 		System.out.println(username("u__hello_world123"));
  12. 		System.out.println(username("aa_"));
  13. 	}
  14. }
Success #stdin #stdout 0.11s 52336KB
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Standard input is empty
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true
false
https://ideone.com/FcGISJ
language:
Java (HotSpot 12)
created:
1 year ago
visibility:
secret

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