How to find the length of longest subString from Java String ?

Below is the example for finding out the longest subString with no repetition in java subString.........

public class LongestSubStringWithNoRepetition {

public static void main(String args[]) {

int x = lengthOfLongestSubstringNoRepetitions("Hi, this is a tesgft string.jgdfgdfkhfjrestjkbngfld ");
System.out.println(""+x);

}

public static int lengthOfLongestSubstringNoRepetitions(String s) {

   if (s == null)
       return 0;

   // Trimming input even for the non-empty case is more consistent.
   final String str = s.trim();

   if (str.equals(""))
       return 0;

   int seen[] = new int[Character.MAX_VALUE+1];
   for (int i = 0; i <= Character.MAX_VALUE; ++i)
       seen[i] = -1;

   int max = 1;
   int len = 0;

   for (int j = 0; j < str.length(); ++j) {
       char ch = str.charAt(j);
       // If ch was recently seen,
       // counting must restart after the last place it was seen.
       // Otherwise, it adds 1 to the length.
       len = Math.min(j-seen[ch], len+1);
       if (len > max)
           max = len;
       seen[ch] = j;
   }
   return max;
}

}

Below is the output........

12