CODEWITHSUNDEEP
java
Ralph
Ralph

Reputation: 195

Output the contents of an ArrayList as a comma-separated String

I am attempting to add a comma separator to the String representation of a Java ArrayList but nothing seems to work, I am obviously missing something simple.

Sadly old Java 6 (running in a JSP):

ArrayList zones= new ArrayList();
zones.add(pageContext.getAttribute("zone"));

for(int i=0; i<zones.size(); i++)
out.println(zones.get(i));

// output is   CellA116 CellA116 CellA116 Reception Reception CellA11

StringBuffer stringBuffer = new StringBuffer();
for(int i=0; i<zones.size(); i++)
{
stringBuffer.append(zones.get(i));
stringBuffer.append(",");
}

out.println(stringBuffer.toString());

// output is   CellA116,CellA116,CellA116,Reception,Reception,CellA11,  (commas)

  %>     

</tr>
</c:forEach>

syntax wont work here (outside of loop)
out.println(stringBuffer.substring(0, stringBuffer.length() - 1));

I need to remove the final comma (as I eventually want to use the array in chart.js), appreciate any thoughts.

Upvotes: 1

Views: 1617

Answers (3)

DaveyDaveDave
DaveyDaveDave

Reputation: 10562

Generally speaking, relying on a toString() method to do this is an easy way to inadvertently introduce bugs later on. If you change what concrete class is providing the collection (maybe to a Set instead of a List for example), your assumption that it starts and ends with square brackets might be untrue, and your output might change without you realising it.

I'd suggest that a more appropriate solution would be to iterate over the collection of Strings and add them to a StringBuilder.

So, it might look something like:

StringBuilder stringBuilder = new StringBuilder();
for(int i=0; i<strList.size(); i++)
{
    stringBuilder.append(strList.get(i));
    stringBuilder.append(",");
}

// Remove the last character from the StringBuilder to avoid a trailing comma.
String commaSeparatedList = stringBuilder.substring(0, stringBuilder.length() - 1);

out.println(commaSeparatedList);

Upvotes: 2

deHaar
deHaar

Reputation: 18568

You can utilize a StringBuilder and a classic for loop to output a csv line from List<String>.

Have a look at this:

public static void main(String args[]) {
    List<String> zones = new ArrayList<String>();
    zones.add("CellA116");
    zones.add("CellA116");
    zones.add("CellA116");
    zones.add("Reception");
    zones.add("Reception");
    zones.add("CellA11");

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < zones.size(); i++) {
        if (i < zones.size() - 1) {
            sb.append(zones.get(i)).append(";");
        } else {
            sb.append(zones.get(i));
        }
    }

    System.out.println(sb.toString());
}

The output will look like this:

CellA116;CellA116;CellA116;Reception;Reception;CellA11

If you want to have a method with a flexible separator char, then use something like this:

public static String toSeparatedString(List<String> values, char separator) {
    StringBuilder sb = new StringBuilder();

    for (int i = 0; i < values.size(); i++) {
        if (i < values.size() - 1) {
            sb.append(values.get(i)).append(separator);
        } else {
            sb.append(values.get(i));
        }
    }

    return sb.toString();
}

Upvotes: 2

Prabhu
Prabhu

Reputation: 129

I dont see the need for another for loop to replace the [] and , zones.toString().replaceAll("[\[\]\s]", "") suggested by Lino works well.

Upvotes: -2

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