Join a list of object's properties into a String

Question

I'm learning lambda right now, and I wonder how can I write this code by a single line with lambda.

I have a Person class which includes an ID and name fields

Currently, I have a List<Person> which stores these Person objects. What I want to accomplish is to get a string consisting of person's id just like.

"id1,id2,id3".

How can I accomplish this with lambda?

Answer 1

To retrieve a String consisting of all the ID's separated by the delimiter "," you first have to map the Person ID's into a new stream which you can then apply Collectors.joining on.

String result = personList.stream().map(Person::getId)                           .collect(Collectors.joining(",")); 

if your ID field is not a String but rather an int or some other primitive numeric type then you should use the solution below:

String result = personList.stream().map(p -> String.valueOf(p.getId()))                           .collect(Collectors.joining(",")); 

Answer 2

stream to map, and collect to list!

List<String> myListofPersons = personList.stream()           .map(Person::getId)           .collect(Collectors.toList()); 

if you need that in a String object then join the list

String res = String.join(" , ", myListStringId); System.out.println(res);