Java StringTokenizer, empty null tokens

https://stackoverflow.com/questions/2708591

01-10-2019
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Question

I am trying to split a string into 29 tokens..... stringtokenizer won't return null tokens. I tried string.split, but I believe I am doing something wrong:

String [] strings = line.split(",", 29);

sample inputs:

10150,15:58,23:58,16:00,00:00,15:55,23:55,15:58,00:01,16:03,23:58,,,,,16:00,23:22,15:54,00:03,15:59,23:56,16:05,23:59,15:55,00:01,,,,
10155,,,,,,,,,,,07:30,13:27,07:25,13:45,,,,,,,,,,,07:13,14:37,08:01,15:23
10160,10:00,16:02,09:55,16:03,10:06,15:58,09:48,16:07,09:55,16:00,,,,,09:49,15:38,10:02,16:04,10:00,16:00,09:58,16:01,09:57,15:58,,,,

Solution

If you want the trailing empty strings to be kept, but you don't want to give a magic number for maximum, use a negative limit:

line.split(",", -1)

If line.equals("a,,c"), then line.split(",", -1)[1].isEmpty(); it's not null. This is because when "," is the delimiter, then ",," has an empty string between the two delimiters, not null.

Example:

Using the explanation above, consider the following example: ",,"

Although you might expect ",", null, and ",".

The actual result is ",", "" and ","

If you want null instead of empty strings in the array returned by split, then you'd have to manually scan the array and replace them with null. I'm not sure why s == null is better than s.isEmpty(), though.

public static String[] splitTotokens(String line, String delim){
  String s = line;
  int i = 0;

  while (s.contains(delim)) {
  s = s.substring(s.indexOf(delim) + delim.length());
      i++;
  }
  String token = null;
  String remainder = null;
  String[] tokens = new String[i];

  for (int j = 0; j < i; j++) {
    token = line.substring(0, line.indexOf(delim));
    //System.out.print("#" + token + "#");
    tokens[j] = token;
    remainder = line.substring(line.indexOf(delim) + delim.length());
    //System.out.println("#" + remainder + "#");
    line = remainder;
    }

  return tokens;`  
 }

If you want empty tokens to be retained string.split() won't work satisfactorily. StringTokenizer will also not work. I have come with following method, which might be helpful for you:

public static String[] splitTotokens(String line, String delim){
    String s = line;
    int i = 0;

    while (s.contains(delim)) {
        s = s.substring(s.indexOf(delim) + delim.length());
        i++;
    }
    String token = null;
    String remainder = null;
    String[] tokens = new String[i];

    for (int j = 0; j < i; j++) {
        token = line.substring(0, line.indexOf(delim));
        // System.out.print("#" + token + "#");
        tokens[j] = token;
        remainder = line.substring(line.indexOf(delim) + delim.length());
        //System.out.println("#" + remainder + "#");

        line = remainder;
    }
    return tokens;
}

use this org.springframework.util.StringUtils

org.springframework.util.StringUtils.delimitedListToStringArray(data, delimit);

This class delivers some simple functionality provides easy-to-use methods to convert between delimited strings, such as CSV strings, and collections and arrays.

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Java StringTokenizer, empty null tokens

See also