String token

[Jackie Wang]

IF I have a long html string like
String code = "<table cellspacing=\"0\" border=\"0\" cellpadding=\"5\"> <tr> <td class=\"headingImageBox\" align=\"center\"><b>2000 GMC Yukon XL</b> </td> </tr> <tr> <td align=center class=\"contentImageBox\">First Row<br> <img src=\"../../../images/2000-gmc-suburban/1strow/main_ip_im.jpg\" width=350 usemap=\"#mainip2000-gmc-suburban\" border=\"0\"><br> <a href=\"#top\"><img src=\"../../../html_images/top_of_page.gif\" width=\"100\" height=\"19\" border=\"0\"></a><map name=\"mainip2000-gmc-suburban\"><area shape=\"rect\" coords=\"82,109,111,138\" href=\"#steering\" target=\"_self\"><area shape=\"rect\" coords=\"168,88,197,117\" href=\"#stereo\" target=\"_self\"><area shape=\"rect\" coords=\"263,92,292,121\" href=\"#gl "
i wanna write a method to replace all the gif to jjpg. What's the most efficient way to do that?
Thanks!

[Jessica Sant]

Here's my guess -- not guaranteed to be most efficient:
1- Convert to a StringBuffer(String creation is very expensive -- much more efficient to do string manipulation in a StringBuffer)
2- Search through the String for the location of .gif with String.indexOf(String asdf) -- because .jpg and .gif have the same # of characters -- the location will be the same after you start substituting things
3- use the StringBuffer.replace(int start, int end, String replace) to swap the characters.
thoughts?

[Rene Larsen]

If you are using JDK 1.4.x then there is a new String method - 'replaceAll' - try read this link:
http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html
/Rene
[ July 17, 2002: Message edited by: Rene Larsen ]

[Jackie Wang]

I am using 1.3 instead.
How about if I wanna change to jpeg instead of jpg which have different char?
Thanks so much for help

[Rene Larsen]

You can use this method I've made:

public String replaceStringWithString(String srcStr, String oldStr, String newStr) {
   while (srcStr.indexOf(oldStr) > -1) {
      if (!(srcStr.equals(newStr))) {
         int i = srcStr.indexOf(oldStr);
         String firstStr = null;
         String restStr = null;
         if (i != -1) {
            firstStr = srcStr.substring(0, i);
            int index = srcStr.indexOf(oldStr) + oldStr.length();
            if (index <= srcStr.length()) {
               restStr = srcStr.substring(index);
            }
            StringBuffer sb = new StringBuffer();
            sb.append(firstStr).append(newStr).append(restStr);
            srcStr = sb.toString();
         }
         else {
            return srcStr;
         }
      }
   }
   return srcStr;
}

and then call it like this:

String strTest = "this is test.gif";
String tmpStr = replaceStringWithString(strTest, ".gif", ".jpg");

/Rene

[Jackie Wang]

Thanks Rene! Efficient method!

[Jim Yingst]

Ermmm... I can't help noticing that a new StringBuffer is being created each time through the loop. And the first part of the input string is getting re-searched for the target substring on every iteration as well. Once you've replaced all occurances of the target up to a given index currentPos, you really only need to search the remaining string for additional occurances:
int index = srcStr.indexOf(oldStr, currentPos);
Here's my version (for when Java 1.4 is unavailable):

  public static String replace(String input, String fromStr, String toStr)
  {
    // preconditions:
    if (input == null)
      throw new NullPointerException("input is null");
    if (fromStr == null)
      throw new NullPointerException("fromStr is null");
    if (toStr == null)
      throw new NullPointerException("toStr is null");
    if (fromStr.length() == 0)
      throw new IllegalArgumentException("fromStr is empty (\"\")");
 
    int nextFromStrPos = input.indexOf(fromStr);
    if (nextFromStrPos < 0)
      return input; // return early if no replacement is necessary
 
    StringBuffer buffer = new StringBuffer();
    int currentPos = 0;
    while (currentPos < input.length())
    {
      if (nextFromStrPos >= 0)
      {
        // copy everything up to fromStr:
        buffer.append(input.substring(currentPos, nextFromStrPos));
        // replace fromStr with toStr:
        buffer.append(toStr);
        currentPos = nextFromStrPos + fromStr.length();
      }
      else
      {
        // copy remaining text
        buffer.append(input.substring(currentPos));
        currentPos = input.length(); // done
      }
      nextFromStrPos = input.indexOf(fromStr, currentPos);
    }
    return buffer.toString();
  }

[ July 18, 2002: Message edited by: Jim Yingst ]

[Rene Larsen]

Here is my modyfied/optimized version:

public String replaceStringWithString(String srcStr, String oldStr, String newStr) {
   StringBuffer sb = new StringBuffer();
   int pos = srcStr.indexOf(oldStr);
   if (pos == -1) {
      return srcStr;
   }
   while (pos > -1) {
      sb.append(srcStr.substring(0, pos)).append(newStr);
      int index = pos + oldStr.length();
      if (index <= srcStr.length()) {
         srcStr = srcStr.substring(index);
      }
      pos = srcStr.indexOf(oldStr);
   }
   sb.append(srcStr);
   return sb.toString();
}

Jim, thank you for your feedback.
/Rene
[ July 18, 2002: Message edited by: Rene Larsen ]