Using Java 8 to convert a list of objects into a string obtained from the toString() method

Question

There are a lot of useful new things in Java 8. E.g., I can iterate with a stream over a list of objects and then sum the values from a specific field of the Object

Answer 1

One simple way is to append your list items in a StringBuilder

   List list = new ArrayList<>();
   list.add(1);
   list.add(2);
   list.add(3);

   StringBuilder b = new StringBuilder();
   list.forEach(b::append);

   System.out.println(b);

you can also try:

String s = list.stream().map(e -> e.toString()).reduce("", String::concat);

Explanation: map converts Integer stream to String stream, then its reduced as concatenation of all the elements.

Note: This is normal reduction which performs in O(n²)

for better performance use a StringBuilder or mutable reduction similar to F. Böller's answer.

String s = list.stream().map(Object::toString).collect(Collectors.joining(","));

Ref: Stream Reduction