将多个字符串合并为一个 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,

Answer 1

It is better to use StringBuilder

 StringBuilder sb= new StringBuilder();

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

Answer 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()

Answer 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();

Answer 4

Maybe you are looking only for

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

Reference

Answer 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);

Answer 6

Alternatively, if you are using Java 8, you could try something like this:

public static String join(final Set<String> set){
    return new StringBuilder(",").append(set.stream().collect(Collectors.joining(",,"))).append(",").toString();
}

public static void main(String args[]){
    Set<String> setInput = new TreeSet<>();
    setInput.add("Dog");
    setInput.add("Cat");
    setInput.add("Mouse");
    System.out.println(join(setInput));
}

The output is:

,Cat,,Dog,,Mouse,

Although, I'm a little unsure to why you would want 2 commas in between each element and a comma at the start and end. If you just want one comma separating each element (and no comma at the start or end), modify the join(Set<String>) to look like this:

public static String join(final Set<String> set){
    return set.stream().collect(Collectors.joining(",")); //change "," to ", " for spacing
}

After doing so, the new output would be:

Cat,Dog,Mouse

Answer 7

org.apache.commons.lang.StringUtils.join() 可以派上用场