• Frequently:
  • We need to create a String that contains (and/or print) multiple items in a "collection" with a delimiter between items (but not before the first or after the last)
• General Examples:
  • Comma-Separated-Value (CSV) Format
  • Space (or Tab) Delimited Lines
• A Specific Example:
  • Creating the String object "Rain,Sleet,Snow" from a String[] containing the three words
• An Important Point:
  • We can't work with all of the elements at once so we can't use a format String

• The Issue:
  • Not all solutions that are correct are elegant
• Different Perspectives/Descriptions:
  • There is a delimiter between every pair of items
  • There is a delimiter after every item except the last item and the first item when there is only one
  • There is a delimiter before every item except the first item (which is also the last item when there is only one)

• One Way for the Code to Vary:
  • Put a delimiter after an item when there is another to item come
  • Put a delimiter before an item when there was already an item
• Another Way for the Code to Vary:
  • Handle item 0 as a special case or not

javaexamples/programmingpatterns/DelimitingStrings.java (Fragment: 10)

        // Append the delimiter when needed
        result = "";        
        for (int i = 0; i < item.length; ++i) {
            result += item[i];
            if (i < item.length - 1) {
                result += delim;
            }
        }
        

javaexamples/programmingpatterns/DelimitingStrings.java (Fragment: 11)

        // Append the delimiter when needed, initializing
        // the accumulator based on the length
        if (item.length > 1) {
            result = item[0] + delim;
        } else if (item.length > 0) {
            result = item[0];
        } else {
            result = "";
        }
        
        for (int i = 1; i < item.length - 1; ++i) {
            result += item[i];
            result += delim;
        }

        if (item.length > 1) {
            result += item[item.length - 1];
        }
        

javaexamples/programmingpatterns/DelimitingStrings.java (Fragment: 12)

        // Prepend the delimiter when needed
        result = "";        
        for (int i = 0; i < item.length; ++i) {
            if (i > 0) {
                result += delim;
            }
            result += item[i];
        }
        

• Comparison:
  • You might not have a preference between appending and prepending
• A Slightly Different Requirement:
  • You need to be able to use a different delimiter before the last element (e.g., "Rain, Sleet, and Snow")
• The Resulting Preference:
  • The append approach doesn't require a nested if statement

• Approach:
  • Append
• Method Signatures:
  • Include one with one delimiter and one with two delimiters

javaexamples/programmingpatterns/DelimitingStrings.java (Fragment: pattern)

    /**
     * Create a delimited String from a String[].
     *
     * @param item   The items to include
     * @param delim  The delimiter to place between all but the last two items
     * @param lastdelim  The delimiter to place between the last two items
     * @return The delimited String
     */
    public static String toDelimitedString(String[] item, 
                                           String delim, String lastdelim) {
        String result;

        result = "";        
        for (int i = 0; i < item.length; ++i) {
            result += item[i];
            if (i  < item.length - 2) {
                result += delim;
            }  else if (i == item.length - 2) {
                result += lastdelim;
            }
        }
        return result;
    }

    /**
     * Create a delimited String from a String[].
     *
     * @param item   The items to include
     * @param delim  The delimiter to place between the items
     * @return The delimited String
     */
    public static String toDelimitedString(String[] item, String delim) {
        return toDelimitedString(item, delim, delim);
    }
        

• The Oxford Comma:
  • "rain, sleet, and snow" rather than "rain, sleet and snow"
• Using the Pattern:
  • Pass ", " as delim
  • Pass ", and " as lastdelim