Home > Java > Extending and the improving the token location method

Extending and the improving the token location method

I have been busily building up the methods which surround the token location method I outlined in yesterday’s post since I aim to build a robust StringBuffer/Builder helper class which is as flexible and intuitive as the locator methods expressed in the standard Java String class.

Obviously one thing I will want to do with the method outlined previously is to build a stripped down version which only iterates the String to search once for handling short token matches. And I’ll obviously need to determine the criteria for deciding under what circumstances to use which of the two eventual implementations of this method I arrive at. The NetBeans profiling tool is an obvious win here for examining assets such as memory and heap usage, and I have a nice little wrap-around timer utility which I can inject into my class for assessing relative speeds of differently constructed search parameters passed as arguments. I’ll have a look at it over the weekend and once that’s out of the way and the appropriate method is being called by a delegator method, I’ll optimise some of the syntax candy which I am already beginning to surround this method with. None of the methods are particularly pretty or built at this stage for speed, they’re built for facility of implementation and can be used as is pretty much out of the box.

The obvious initial methods to sugar up are ones which can use the generated List object e.g. the trivial (and inefficient) countTokens method & its overload which follows:


/** Syntax candy to count the number of incidences of a token in a given char sequence */

public int countTokens(StringBuffer sb, StringBuffer sbx)
    {
            List<Integer> l = findTokens(sb, sbx);
            return l.size();
     }

/** Syntax candy ph to count the number of incidences of a token (expressed as items) in a given List */

public int countTokens(List<Integer> l)
    {
            return l.size();
     }

Next up there’s a standard boolean check to see whether there are any matched tokens:


public boolean containsMatch(StringBuffer sb, StringBuffer sbx)
    {
    if (countTokens(sb, sbx) < 1 )
        {
        return false;
        }
    return true;
    }

OK that’s the rough & ready syntax candy out of the way, now let’s look at how we can leverage the information we have back in the List. Examining large strings (& this is particularly the case with large strings arriving from or in markup language formats such as HTML/XML etc)  it’s often the case that you need to know about the position of  either a single char relative to the token’s position, or alternatively another token altogether. The char based implementations for forward and reverse location are relatively simple. They both take the String to search, the offset character index point and the char which needs to be located as arguments, and look like this:


public int findPreviousMatch(StringBuffer sb, int startPt, char toLocate)
    {
    int loc = -1;
    int ctr = startPt;
    while (ctr >= 0)
    {
            ctr--;
            if (sb.charAt(ctr) == toLocate)
            {return ctr;}
    }
    return loc;
    }

public int findNextMatch(StringBuffer sb, int startPt, char toLocate)
    {
    int loc = -1;
    int ctr = startPt;
    int len = sb.length();
    while (ctr < len)
    {
            ctr++;
            if (sb.charAt(ctr) == toLocate)
            {return ctr;}
    }
    return loc;
    }

We need to do the same thing for tokens. Arguments are an int indicating the starting point to search around, the StringBuffer to search (sb) and the token to search for (sbx) expressed again as a StringBuffer.


public int findTokenPriorToOffset(int start, StringBuffer sb, StringBuffer sbx)
    {
    int loc = -1;
    if (start > sb.length())
    {start = sb.length();} // move start to be the sb.length() if start > the size of inc string

    int pos = start;
    List<Integer> l = findTokens(sb, sbx);
    if(l.size() == 0){return loc;} // no match

    // only 1 item and bigger than start? return -1
    if ((l.size() == 1) && ((Integer) l.get(1) > start) )
    {
       return loc;
    }
    // only 1 item and less than start? return token startpoint
    if ((l.size() == 1) && ((Integer) l.get(1) < start) )
    {
       return (Integer) l.get(1);
    }

    Iterator it = l.iterator();
    while(it.hasNext())
    {
    int val = (Integer) it.next();
    if (val > start){return loc;}
    if (val < start)
    {
        loc = val;
    }

    }

    return loc;
}
public int findTokenAfterOffset(int start, StringBuffer sb, StringBuffer sbx)
    {
    int loc = -1;
    if (start > sb.length())
    {        return  -1; } // won't be found.... ret -1

    int pos = start;
    List<Integer> l = findTokens(sb, sbx);
    if(l.size() == 0){       return loc; }  // no match

    // only 1 item and less than start? return -1
    if ((l.size() == 1) && ((Integer) l.get(1) < start) )
    {
       return loc;
    }
    // only 1 item and &gt; start? return token startpoint
    if ((l.size() == 1) && ((Integer) l.get(1) > start) )
    {
       return (Integer) l.get(1);
    }
    Iterator it = l.iterator();
   

 while(it.hasNext())
    {
    int val = (Integer) it.next();
       if (val > start){return val;}
    }
    // fallthrough
    return loc;
}

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