How can I concatenate string elements from list in java8 based on their amount? - java-8

Question

I have the following structure:
class MyClass {
String name;
String descr;
public String getName() {
return name;
}
}
Now I have a List of those objects and I want to print the name from the object above if the list contains any of those elements.
This is my code so far:
List<MyClass> list = getList();
if (list != null && list.size() > 0) {
System.out.println(list.get(0).getName());
} else {
System.out.println("list is empty");
}
This will work when the list contains only one element. Now I need to improve it and consider an example when there is more than one element - in that case I need to print all names, comma separated.
For example the output should be:
When there are 3 elements:
name1,name2,name3
when there's one element:
name1
and when there's none:
list is empty
what's the most efficient way of implementing it?

Answer 1

You could use Collectors.joining combined with Collectors.collectingAndThen:
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.joining;
...
String res =
list.stream()
.map(c -> c.name)
.collect(collectingAndThen(joining(","), s -> s.isEmpty() ? "list is empty" : s));
If you want to take in account the option when the list is null, you could do:
String res =
Optional.ofNullable(list).map(l -> l.stream()...).orElse("list is empty");
but to be honest I would use an if statement beforehand:
if(list == null || list.isEmpty()) {
return "list is empty";
} else {
return list.stream().map(c -> c.name).collect(joining(","));
}

Answer 2

You also can use the built-in class StringJoiner to simplify your code as following code:
StringJoiner joiner = new StringJoiner(",");
joiner.setEmptyValue("list is empty");
list.forEach(it -> joiner.add(it.getName()));
System.out.println(joiner);