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Thread: A while-loop is SUPPOSED to replace a substring

  1. #1
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    Default A while-loop is SUPPOSED to replace a substring

    I notice that my method doesn't work even though I tried to get it's while-loop set-up to do the following things:

    1. Have each token of a string get put into another one
    2. Replace each given-substring (string2) with it's assigned-replacement (string3) as the string's (string1) tokens pass by
    3. Have it's final answer returned as a variable to the main-method


    Here is my code that has each of it's parts with a comment...

         // For the replacement of a substring with another one.
         public static String replaceSubstring(String string1, String string2, String string3)
         {
              Scanner keys = new Scanner(System.in);
     
              // Use a StringTokenizer-object for breaking a string
              // down to the point of finding that matching-substring
              // in general.
              StringTokenizer numOne = new StringTokenizer(string1, " ", true);
              StringTokenizer num1 = new StringTokenizer(string1, " ", true);
              StringTokenizer numWon = new StringTokenizer(string1, " ", true);
     
              String attacher = new String();
     
              // Find the substring with the while-loop.
              while (numOne.hasMoreTokens())
              {
                   if (num1.nextToken() == string2)
                   {
                        attacher += string3;
                   }
                   if (numWon.nextToken() != string2)
                   {
                        attacher += numWon.nextToken();
                   }
              }
     
              // Finally, return the String-object.
              return attacher;
         }

    ...and here is the output-part I want to avoid at runtime.

     

    Exception in thread "main" java.util.NoSuchElementException
    at java.util.StringTokenizer.nextToken(StringTokenize r.java:349)
    at MiscellaneousStr.replaceSubstring(MiscellaneousStr .java:93)
    at MiscellaneousSDemo.main(MiscellaneousSDemo.java:84 )




    So as you can see, I have to avoid getting a message that refers to having no more elements in an enumeration.

    Any suggestions?

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  3. #2
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    Default Re: A while-loop is SUPPOSED to replace a substring

    numOne does not "move". You never consume tokens from it. Hence, while's condition is always true. In contrast, numWon and num1 "move" through 1 token in each iteration. Naturally, in an infinite loop, they stumble upon the last element one day. When that day comes, they have no more element to consume and throw exception.

    And, this implementation is a bad practice. You can use just one tokenizer for all your needs, not 3.
    StringTokenizer oneAndOnly = //blahblahblah
     
    while(oneAndOnly.hasMoreTokens()) {
      String next = oneAndOnly.nextToken();
      if(next == string1) attacher += string3;
      else attacher += next; //or oneAndOnly.nextToken(), depending on your needs.
    }

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    SOG (May 29th, 2013)

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    Default Re: A while-loop is SUPPOSED to replace a substring

     if (num1.nextToken() == string2)

    And use the equals method when comparing String objects.

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    SOG (May 29th, 2013)

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    Default Re: A while-loop is SUPPOSED to replace a substring

    I got past the part where there are too many elements, but I still need help finding the word-replacement substring for the program.

    Here is my current code-setup:

              // Use the while loop to replace the substring.
              while (numOne.hasMoreTokens()) 
              { 
                  String next = numOne.nextToken(); // Use the next-string to not overuse the nextToken-method.
     
                  // If next is the same as string2, then tack on string3 to the attacher-string...
                  if (next == string2) 
                  {
                       attacher += string3;
                  } 
     
                  // ...or else you should tack on the next token of string1/next.
                  else
                  {
                       attacher += next;
                  }
              }

    Are there any suggestions now relative to the logic here?

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  9. #5
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    Default Re: A while-loop is SUPPOSED to replace a substring

    The problem I should've mentioned is that the current loop I have now just makes my method return the same string-statement I typed in as a user.

    For example:

    The program's output comes as a command and the mine is the response.

     

    Type in a word to replace in a string for later

    this

    Now type in a word to replace that word with

    that

    Now type that string

    this and that

    Your new string is this: this and that



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  11. #6
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    Default Re: A while-loop is SUPPOSED to replace a substring

    if (next == string2)
    Don't use == to compare objects, use the equals method instead.
    Improving the world one idiot at a time!

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    SOG (May 29th, 2013)

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    Default Re: A while-loop is SUPPOSED to replace a substring

    Thanks. I finally got the needed response from the computer with the equals-method's help.

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