Combine multiple strings into one JAVA

Question

I have a set of strings which want to combine into one String with all sentences separated with coma like (*.csv)

here is how it goes with me:

String dataContainer;

for(String tempString:setInput){
     String finalString = "," + tempString + "," ;   
}

This doesn't work with me :(
But it should do for Set ex:

Set<String> setInput = new TreeSet();
setInput.add("Dog");
setInput.add("Cat");
setInput.add("Mouse");

to produce the string:

,Dog,,Cat,,Mouse,

Solution 1

It is better to use StringBuilder

 StringBuilder sb= new StringBuilder();

for(String tempString:setInput){
   sb.append(",").append(tempString).append(",");   
 }

Solution 2

Or we can use Java 8 Stream

String joined = Stream.of("A", "B", "C").collect(Collectors.joining("delimiter", "prefix", "suffix"));

Or use the StringJoiner class

Directly Use StringJoiner class

Or the StringBuilder class

new StringBuilder().add("A").add("B").toString()

Solution 3

What You are doing is intializing your result string each time.

Actually ,you want to do

String finalString ="";
for(String tempString:setInput){
      finalString += "," + tempString + "," ;   
}

But the above approach causes multiple String creations.

But I suggest to go for StringBuilder.

 StringBuilder finalStringb =new StringBuilder();
    for(String tempString:setInput){
          finalStringb.append(",").append(tempString).append(",") ;   
    }

String finalS = finalStringb.toString();

Solution 4

Maybe you are looking only for

String csvString = "," + String.join(",,", string1, string2, string3) +"," ;

Reference

Solution 5

Solution 1: (If you don't need a delimiter)

---

I would recommend using concat(Object... objects) from org.assertj.core.util.String.

public static String concat(Object... objects) {
    return Arrays.isNullOrEmpty(objects) ? null : (String)java.util.Arrays.stream(objects).map(String::valueOf).collect(Collectors.joining());
}

You can use it like this:

  concat("string1", "string2", "string3", "string4");

Solution 2 using StringJoiner (Java 8+):

---

This is from java.util. You even have the option to specify a prefix and suffix.

StringJoiner stringJoiner = new StringJoiner(", ");
 
stringJoiner.add("string1");
stringJoiner.add("string2");
stringJoiner.add("string3");
 
assertEquals("string1, string2, string3", stringJoiner.toString());

Solution 3 using Collectors.joining (Java 8+):

---

This is a functionality from Java 8 Stream API.

List<String> stringList = Arrays.asList("string1", "string2", "string3");
 
String concatString = stringList.stream().collect(Collectors.joining(", "));
 
assertEquals("string1, string2, string3", concatString);

View more solutions

Comments

[Pshemo]

or even sb.append(",").append(tempString).append(",");

[Ruchira Gayan Ranaweera]

@Pshemo yes, it is better. I added your suggestion.

[Nandkumar Tekale]

+1 you can delete last inserted comma using sb.deleteCharAt(sb.lastIndexOf(",")); if it is not necessary

[simoconfa]

String finalS = finalStringb.toString() really helps me!

[O.O.Balance]

Won't match the desired output of ,Dog,,Cat,,Mouse,.

[Dalton]

Okay so String csvString = "," + String.join(",,", string1, string2, string3) +"," ;

[Rituraj]

code for removing of last delimiter (comma in this case) doesn't looks kind of old school, I would suggest StringJoiner or StringJoiner through java streams as I mentioned in the answer below. That has nice aesthetics :)

[Ruchira Gayan Ranaweera]

@Rituraj it is up to you to decide. if you are going for Java 8 yes. you can. This question originally posted even before Java 8.

[Rituraj]

Yeah. I know it was an old question, I just tried to provide a context, in case someone is using later versions of java. For prior versions I generally preferred Guava from google