Method using StringBuffer for deleting dups

Question

I'm writing a method for deleting dups from a String using StringBuffer. The method is returning StringIndexOutOfBoundsException. How can I fix it ?

public static void removeDups( String myString ){

        StringBuffer sb = new StringBuffer( myString );
        int len =  myString.length(); 

        for ( int j = 0; j < len; j++ ){

            char c = sb.charAt(j);

            for ( int k = len - 1 ; k > j ; k-- ){

                if ( sb.charAt(k) == c ){

                    sb.deleteCharAt(k);
                    len--; 
                }

            }
        }

        System.out.println("After deleting the dups : " + sb.toString() ); 
    }

Technically, it isn't returning StringIndexOutOfBoundsException it is throwing it. For future references. — Emz
– Emz, Commented Aug 3, 2015 at 19:27

Louis Wasserman · Accepted Answer · 2015-08-03 19:27:45Z

3

for (int k = len - 1 ; k > j ; k++ )

If you're trying to iterate downwards, it needs to be k--, not k++. Right now, the second iteration is going to have k = len, and that's out of bounds. You're updating upwards infinitely instead of down to a bound.

You're also missing a bracket: it needs to be

 if ( sb.charAt(k) == c ) {
    sb.deleteCharAt(k);
    len--; 
 }

(While we're at it, there is essentially no reason ever to use StringBuffer instead of StringBuilder, which provides ~the same API without synchronization overhead.)

edited Aug 3, 2015 at 19:27

answered Aug 3, 2015 at 19:09

Louis Wasserman

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3 Comments

Monica Hübner Over a year ago

Yes, that's correct. I changed it, but, still the method deletes one repetition. Say, when I put "njznj" it will print "njzj".

Monica Hübner Over a year ago

Thanks for mentioning about the bracket. I also write some Python and thought it will cover two lines without the bracket. Now, the program is fine and thanks for your effort.

mihi Over a year ago

and "while we're at it", deleting characters (or short substrings) from StringBuilder repeatedly is almost always a lot slower than copying the parts that should remain, as delete will have to move all the text after the deletion point.

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