Java ArrayList StringBuilder appending

Question

I have one problem when appending List values as String. I will be getting 1 or more than 1 value into the list. Then I need to append these string as one string and use a separator , for each string. But at the end also the comma is getting added. How Can I remove this at the end of the string dynamically. Here is my code:

cntList = parseXml(metadata.xml);
if (cntList.size() != 0) {
    // entryCountryMap.put(id, country);
    System.out.println("Size is  ---->" + cntList.size());
    StringBuilder sb = new StringBuilder();
    if (cntList.size() >= 2) {
        for (String s : cntList) {
            sb.append(s);
            sb.append(",");
        }
    }
    System.out.println("StringBuilder ----->" + sb.toString());
}

And my output is like this:

StringBuilder ----->All Countries,US - United States,

Please help me resolving this. Thanks - Raji

What you are looking for is called Joining a string. This is explained here: Java: convert List<String> to a joined string — Thirler
– Thirler, Commented Jul 8, 2015 at 13:27

Simon · Accepted Answer · 2015-07-08 15:23:17Z

8

With java 8 it's a one liner

String.join(",", cntList);

If you need to filter the elements of the list and/or mutate the strings before joining to a single string, you can still do it in a very concise manner without loops.

cntList.stream().filter(...).map(...).collect(Collectors.joining(","));

(the ... need to be replaced by your filtering predicate and your mapper)

edited Jul 8, 2015 at 15:23

answered Jul 8, 2015 at 13:29

Simon

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4 Comments

maskacovnik Over a year ago

Nice one line solution +1

m4ktub Over a year ago

There is nothing telling Java 8 is being used. Also, if Java 8 is available, a String.join() is superior for this particular situation.

Rajyalakshmi S Over a year ago

@ Simon - Using java 6 version. So I tried the other solution which is working. Thanks anyways.

VGR Over a year ago

Or, more compactly, String.join(",", cntList);. See String.join.

maskacovnik · Accepted Answer · 2015-07-08 13:28:22Z

3

I would use normal for loop. The last one append outside the for loop without comma

if (cntList.size() >= 2) {
    for (int i=0;i<cntList.size()-1;i++) {
        sb.append(cntList.get(i));
        sb.append(",");
    }
    sb.append(cntList.get(cntList.size()-1));
}

answered Jul 8, 2015 at 13:28

maskacovnik

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Comments

Community · Accepted Answer · 2017-05-23 12:24:29Z

1

Simply delete the last character:

StringBuilder sb = new StringBuilder("foo,");
System.out.println(sb.deleteCharAt(sb.length() - 1));

Output

foo

More dynamically, you can find the last comma by index and delete that plus anything that comes after:

sb.delete(sb.lastIndexOf(","), sb.length());

As Pshemo points out:

sb.setLength(sb.length() - 1); will actually perform better than sb.deleteCharAt(sb.length() - 1).

edited May 23, 2017 at 12:24

CommunityBot

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answered Jul 8, 2015 at 13:26

Mena

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3 Comments

Pshemo Over a year ago

From what I remember sb.deleteCharAt(sb.length() - 1) will need to create new copy of old values without last element. It would be faster to simply set reduce length of builder sb.setLength(sb.length() - 1);

Mena Over a year ago

@Pshemo nice thinking. Will add to the answer.

Pshemo Over a year ago

I am not sure what you mean. setLenght will call ensureCapacityInternal which will try to expand array if new capacity is larger, but this is not the case here since we want to reduce it.

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