How to concatenate a string with the new 1.8 stream API

Question

Lets say we have a simple method that should concat all names of a Person collection and return the result string.

public String concantAndReturnNames(final Collection<Person> persons) {
    String result = "";
    for (Person person : persons) {
        result += person.getName();
    }
    return result;
}

Is there a way to write this code with new stream API forEach function in 1 line?

Consider renaming to "concatenate a string scalar property on a collection of pojos" (with the new....) Because your question (and the accepted answer) is beyond "a string" IMHO. Upvote for the question and top answer from me today. — granadaCoder, Aug 08 '22 at 20:48

score 199 · Accepted Answer · edited Dec 05 '18 at 19:20

The official documentation for what you want to do: https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html

 // Accumulate names into a List
 List<String> list = people.stream().map(Person::getName).collect(Collectors.toList());

 // Convert elements to strings and concatenate them, separated by commas
 String joined = things.stream()
                       .map(Object::toString)
                       .collect(Collectors.joining(", "));

For your example, you would need to do this:

 // Convert elements to strings and concatenate them, separated by commas
 String joined = persons.stream()
                       .map(Person::getName) // This will call person.getName()
                       .collect(Collectors.joining(", "));

The argument passed to Collectors.joining is optional.

You may want to use String::valueOf instead of Object::toString to have null safety there. — okutane, Feb 27 '19 at 13:25

How to concatenate a string with the new 1.8 stream API

1 Answers1

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