Question

I am splitting a string by word boundary.

What I am expecting is:

 TOKEN 0  
 TOKEN 1 0
 TOKEN 2  
 TOKEN 3 +Ve

and, what I am getting is,

 TOKEN 0  
 TOKEN 1 0
 TOKEN 2  +
 TOKEN 3 Ve



public void StringExample(){
    String str = " 0 +Ve";

    String[] token = str.split("\\b");

    System.out.println("TOKEN 0 " + token[0]);
    System.out.println("TOKEN 1 " + token[1]);
    System.out.println("TOKEN 2 " + token[2]);
    System.out.println("TOKEN 3 " + token[3]);
}

Can someone give a clue where its going wrong? and Possible corrections if any,

Answer 1

Nothing is going wrong, and the results are as should be expected. Word boundaries match at the before the first character of a String, after the last character of a String and between two characters in the string, where one is a word character and the other is not a word character. The last rule will result in a match between ‘+’ and ‘V’, and so your results make perfect sense.

Perhaps you want to use look ahead and look behind to match anything next to a space. For example:

public class Foo001 {
   // private static final String REGEX1 = "\\b";
   private static final String REGEX2 = "(?= )|(?<= )";

   public static void main(String[] args) {
      String str = " 0 +Ve";

      String[] tokens = str.split(REGEX2);
      for (int i = 0; i < tokens.length; i++) {
         System.out.printf("token %d: \"%s\"%n", i, tokens[i]);
      }

   }
}

This will also match the left of the first space giving an extra token:

token 0: ""
token 1: " "
token 2: "0"
token 3: " "
token 4: "+Ve"