Tokenizing Error java util regex PatternSyntaxException dangling metacharacter

Question

I am using split   to tokenize a String separated with   following this format   name lastName ID school age   name lastName ID school age   name lastName ID school age   I m reading this from a file named  entrada al  using this code   static void leer          try           String ruta  entrada al           File myFile   new File  ruta           FileReader fileReader   new FileReader myFile            BufferedReader reader   new BufferedReader fileReader            String line   null           while   line reader readLine     null               if    line equals                         String    separado   line split         SPLIT CALL                 names add separado 0                    lastNames add separado 1                    ids add separado 2                    ages add separado 3                                     reader close            And I m getting this exception        Exception in thread  main  java util regex PatternSyntaxException  Dangling meta character     near index 0       My guess is that the lack of a   after age on the original text file is causing this  How do I get around it

User · Answer

It is because   is used as a metacharacter to signify one or more occurences of previous character  So if i write M  then it will look for files MMMMMM        Here you are using   as the only character so the compiler is looking for the character to find multiple occurences of so it throws the exception

User · Answer

No  the problem is that   is a reserved character in regexes  so you need to escape it   String    separado   line split             means  zero or more of the previous expression   see the Pattern Javadocs   and you weren t giving it any previous expression  making your split expression illegal  This is why the error was a PatternSyntaxException

User · Answer

The first answer covers it    Im guessing that somewhere down the line you may decide to store your info in a different class structure  In that case you probably wouldn t want the results going in to an array from the split   method   You didn t ask for it  but I m bored  so here is an example  hope it s helpful   This might be the class you write to represent a single person     class Person               public String firstName              public String lastName              public int id              public int age         public Person String firstName  String lastName  int id  int age             this firstName   firstName           this lastName   lastName           this id   id           this age   age                     Add  get  and  set  method if you want to make the attributes private rather than public        Then  the version of the parsing code you originally posted would look something like this    This stores them in a LinkedList  you could use something else like a Hashtable  etc       try        String ruta  entrada al       BufferedReader reader   new BufferedReader new FileReader ruta         LinkedList  60 Person  list   new LinkedList  60 Person          String line   null               while   line reader readLine     null                if    line equals                              StringTokenizer st   new StringTokenizer line                    if  st countTokens      4                            list add new Person st nextToken    st nextToken    Integer parseInt st nextToken     Integer parseInt st nextToken                          else                                whatever you want to do to account for an invalid entry                      in your file   not 4     delimiters on a line   Or you                      could write the  if  clause differently to account for it                               reader close

User · Answer

I had similar problem with regex        It happens for all special characters that have some meaning in a regex  So you need to have      as a prefix to your regex   String    separado   line split

[java] Tokenizing Error: java.util.regex.PatternSyntaxException, dangling metacharacter '*'

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