How to append String to StringBuffer variable in JAVA

Question

My code is as below. i need to add single quotes for each word in string with single quotes after appending DD to it.

public class Main
{
    public static void main(String[] args) {
        String ChkboxIds = "'a1b2c3','321cba','123abc'";
        String checkBoxId = null;
        String checkId = null;
        StringBuilder checkIDS = new StringBuilder("'");
        for(int i=0;i<=ChkboxIds.split(ChkboxIds, ',').length;i++){
            checkBoxId = "DD"+ChkboxIds.split(",")[i].replace("'","")+","+checkBoxId;
            checkId = checkBoxId.substring(0, checkBoxId.length() - 5);
            System.out.println("---PRINT---"+checkId);
            for(int j=0;j<i;j++){
                checkIDS..append('\'').append(checkId.split(",")).append('\'').append(',');
                System.out.println("---PRINT123----"+checkIDS);
            }
        }
    }
}

I have tried using StringBuffer too. please point your answers here. The output i get is some junk data while i need the words with dd attached at the start.

Expected output:'DDa1b2c3','DD321cba','DD123abc'

Answer 1

Problem

• issue at .append(checkId.split(",")) where you append an String[] so it's representation is it's hashcode

• don't need a second loop, each word need one loop round, no inner loop needed

• your split is wrong, you need ChkboxIds.split(","), you don't need with the same string as delimiter

---

Fix

You can do much more simpler than that

• split on comma
• remove quotes, append DD, add quotes
• save at same place in array
• join array with comma

String chkboxIds = "'a1b2c3','321cba','123abc'";

String[] splitted = chkboxIds.split(",");
String checkBoxId;

for (int i = 0; i < splitted.length; i++) {
    checkBoxId = "DD" + splitted[i].replace("'", "");
    splitted[i] = "'" + checkBoxId + "'";
}

String result = String.join(",", splitted);
System.out.println(result);
// 'DDa1b2c3','DD321cba','DD123abc'

Regex power

String chkboxIds = "'a1b2c3','321cba','123abc'";
String result = chkboxIds.replaceAll("'(\\w+)'", "'DD$1'");

Answer 2

Try this:

var ids = Arrays.stream( ChkboxIds.split( "," ) ) // Separate the words
  .map( s -> s.replace( '\'', '' ) ) // Strip the single quotes
  .map( s -> "DD%s".formatted( s ) ) // Prepend with "DD"
  .collect( Collectors.joining( "','", "'", "'" ) );
System.out.println( ids );

Alternatively:

var ids = Arrays.stream( ChkboxIds.split( "," ) ) // Separate the words
  .map( s -> s.replaceFirst( "'", "'DD" ) ) // Replace the first single quote with the prefix
  .collect( Collectors.joining( "," ) );
System.out.println( ids );

Refer to the respective Javadoc for the details.

Answer 3

For a simpler solution, you can try the code below.

public class Main
{
    public static void main(String[] args) {
        String ChkboxIds = "'a1b2c3','321cba','123abc'";
        //Replace all single quotes from the ChkboxIds, split them using comma delimiter, and store it to variable array
        String[] ChkboxIdsNew = ChkboxIds.replace("'","").split(","); 

        String checkIDS = ""; //String variable to be used to store the check ids

        //Loop through the ChkboxIdsNew array
        for (int i = 0; i < ChkboxIdsNew.length; i++) {
            //Only append comma if i is greater than zero
            if (i > 0) {
                checkIDS = checkIDS + ",";
            }
            //Concatenate the single quotes and prefix DD then append it to checkIDS
            checkIDS = checkIDS + "'DD" + ChkboxIdsNew[i] + "'";
        }


        System.out.println(checkIDS);
    }
}

Output:

Answer 4

Using regular expressions: If the single words doesnt contain additional single quotes:

    String ChkboxIds = "'a1b2c3','321cba','123abc'";
    ChkboxIds = ChkboxIds.replaceAll(",'",",'DD").replaceAll("^'","'DD");

Using iteration :

    String arChkBoxIds[]= ChkboxIds.split(",");
    StringBuilder checkIDS1 = new StringBuilder("");
    for (String chkBoxId:arChkBoxIds){
       
       checkIDS1.append("'DD").append(chkBoxId.substring(1)).append(",");
    }
    checkIDS1.setLength(checkIDS1.length()-1);
    System.out.println(checkIDS1);