Recursively append a string to List of String in java

Question

I have a List of String and I would like to append text in front of each String in the list. I am trying to achieve this without a for/Iterator loop like a single line of code. I can't find a solution to this.

Following I have tried with a for loop but need solution without this. Is there a solution?

   List<String> strings = new ArrayList<String>();
                strings.add("a");
                strings.add("b");
                strings.add("c");
            strings.add("d");

List<String> appendedList = new ArrayList<String>();
for (String s : strings) {
    appendedList.add("D" + s);
}

Please help. Thanks.

Answer 1

If you're using Java 8, then you can use the newly added replaceAll method to do this:

strings.replaceAll(s -> "D"+s);

Here's a full working example:

import java.util.Arrays;
import java.util.List;

public class StringTest {
  public static void main(String[] args) {
    List<String> strings = Arrays.asList("a", "b", "c", "d");
    strings.replaceAll(s -> "D"+s);
    System.out.println(strings);
  }
}

You could also use the new Streams API to do this, but slightly more verbosely, making a copy of the list instead of mutating (updating) the original list:

List<String> strings = Arrays.asList("a", "b", "c", "d");
strings = strings.stream()
                 .map(s -> "D"+s) // Using Lambda notation to update the entries
                 .collect(Collectors.toList());
System.out.println(strings);

Note that I used Arrays.asList() to create the list more succinctly. This isn't a new feature in Java 8, so you should be able to use it in Java 5/6/7 as well. Here's my output:

$ java StringTest
[Da, Db, Dc, Dd]

Even if you're not using Java 8 right now, it's still good to note that these features have been added, and if you run into a similar problem in a year or two then you can use something from the new API!

Answer 2

Something like this perhaps

public List<String> recursiveAdd(List<String> strings, List<String> finalList, String prepender){
   if(strings == null || strings.size() == 0) return finalList;
   else{
       finalList.add(prepender + strings.remove(0));
       return recursiveAdd(strings,finalList,prepender);
   }
} 

strings = recursiveAdd(strings, new ArrayList<String>(), "D");

---

This is more a functional solution, the problem with the above code is that strings will be destroyed inside the class you can make a deep copy before calling the recursive operation if you want to avoid that!