Methods to eliminate the last comma from a StringBuilder Object (running in a Loop) in JAVA 7?

Question

Current Output looks like : { "1": "abc", "2": "def", "3": "ghi", }

Expected : { "1": "abc", "2": "def", "3": "ghi" } // No last comma

CODE :

BufferedReader br = new BufferedReader(reader);
String nextLine = ""; 
StringBuilder sb = new StringBuilder();
sb.append("{ \n");
while ((nextLine = br.readLine()) != null) {
    sb.append(...);
    sb.append(",");
    sb.append("\n");
}
sb.append("}");

@leon : I am appending the comma after each line, so looks like { "1": "abc", "2": "def", "3": "ghi", } instead I want to ignore the last comma before appending. — devk, May 29 '15 at 05:45
@MadProgrammer : Input is read from a text file using BufferedReader, trying to convert a text to JSON. — devk, May 29 '15 at 05:47
get the length if it is equal to length(last element) not append comma.. — Ragu, May 29 '15 at 05:54
possible duplicate of [Remove last character of a StringBuilder?](http://stackoverflow.com/questions/3395286/remove-last-character-of-a-stringbuilder) — Alexandre Lavoie, May 29 '15 at 05:57
@MadProgrammer not wanting to use a JSON library as the text file will vary. — devk, May 29 '15 at 07:23
@devk So? Load the text file and create a JSON array out of the contents like everybody else does — MadProgrammer, May 29 '15 at 07:24
@MadProgrammer Okay, could you brief out ? new to this stuff! — devk, May 29 '15 at 07:27
@devk I did have an example, but the question got closed before I could post it. Take a look at [json-simple](https://code.google.com/p/json-simple/) and it's [Encoding examples](https://code.google.com/p/json-simple/wiki/EncodingExamples) — MadProgrammer, May 29 '15 at 07:45

score 7 · Accepted Answer · edited Oct 31 '21 at 18:35

7

You can simply do like -

String nextLine = ""; 
StringBuilder sb = new StringBuilder();
sb.append("{ \n");
while ((nextLine = br.readLine()) != null) {
    sb.append(...);
    sb.append(",");
    sb.append("\n");
}

//avoid IndexOutOfBoundsException
int lastIndexOfComma = sb.lastIndexOf(",");
if (lastIndexOfComma != -1)
   sb.deleteCharAt(lastIndexOfComma);
sb.append("}");

edited Oct 31 '21 at 18:35

yerlilbilgin

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answered May 29 '15 at 06:08

mrsus

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This worked for me at the moment! Thanks :) @MrSuS – devk May 29 '15 at 07:12
Alternatively see this answer: http://stackoverflow.com/a/41282608/363573 – Stephan Dec 22 '16 at 11:58

score 3 · Answer 2 · answered May 29 '15 at 06:09

3

You can use deleteCharAt method

StringBuilder strbuilder = new StringBuilder();
strbuilder.append(" { \"1\": \"abc\", \"2\": \"def\", \"3\": \"ghi\",}");

strbuilder.deleteCharAt(strbuilder.length()-(strbuilder.length()-strbuilder.lastIndexOf(",")));
System.out.println(strbuilder.toString());

This will give the following output

 { "1": "abc", "2": "def", "3": "ghi"}

answered May 29 '15 at 06:09

newstackoverflowuser5555

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1

This works, but building a string just to delete a section later seems very inneficient – Leon May 29 '15 at 06:41
@Leon I agree with your point, this was answered before he post the code. I would chose mbrandeis answer, but that needs a null check and some tweaks – newstackoverflowuser5555 May 29 '15 at 06:48
A solution without `deleteCharAt`: http://stackoverflow.com/a/41282608/363573 – Stephan Dec 22 '16 at 11:58

score 3 · Answer 3 · answered May 29 '15 at 06:09

Ninad's answer is good if you know the length of your input, but in your case you are reading in a loop and may not have that answer beforehand.

In that case, instead of putting a comma after each readline and then handling the odd end-case, you could put the comma before each readline and handle the known start-case.

String nextLine = ""; 
StringBuilder sb = new StringBuilder();
sb.append("{\n");
nextLine = br.readLine();
sb.append(...);
while ((nextLine = br.readLine()) != null) {
  sb.append(",\n");
  sb.append(...);
}
sb.append("\n}\n");

What if the first `br.readLine()` returns null? – Leon May 29 '15 at 06:43 — Leon, May 29 '15 at 06:43

Ninad Pingale · Answer 4 · 2015-05-29T07:39:45.460

1

Please note this is not a best solution , but will work with minimal changes in your code

So to avoid last comma, you can add if condition. When it comes to last index do not add the comma.

Run the loop first to get total count.

int lineCount=0;
while ((nextLine = br.readLine()) != null) {
 lineCount++;
}

After that again run the loop (your existing code with if condition)

int lineNumber=0;
while ((nextLine = br.readLine()) != null) {
    sb.append(...);

    if(lineNumber<lineCount){  // if current line is less that total count      
                               // then only attach comma
      sb.append(",");
    }

    sb.append("\n");
    lineNumber++;
}

edited May 29 '15 at 07:39

answered May 29 '15 at 05:49

Ninad Pingale

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how does this work? could you please brief? – devk May 29 '15 at 07:14
In you question - br.readLine() - what is br ? – Ninad Pingale May 29 '15 at 07:16
oops, forgot to mention, its an object of BufferedReader -> BufferedReader br = new BufferedReader(new FileReader(fileName)); – devk May 29 '15 at 07:20

bobs_007 · Answer 5 · 2015-05-29T06:10:25.997

1

More Dynamic option

       StringBuilder str = new StringBuilder("Test,");
       System.out.println("length = " + str.replace(str.length()-1, str.length(), ""));

Always good to null check before you do replace.

For your specific case

StringBuilder str = new StringBuilder("{"1": "abc", "2": "def", "3": "ghi",}");
System.out.println("length = " + str.replace(str.length()-2, str.length()-1, ""));

edited May 29 '15 at 06:10

answered May 29 '15 at 06:05

bobs_007

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Methods to eliminate the last comma from a StringBuilder Object (running in a Loop) in JAVA 7?

5 Answers5