How Can I Efficiently Join a List of Strings in Java?

Java: Convert List to a Join()d String

In JavaScript, the Array.join() method provides a convenient way to concatenate elements of an array into a single string. Java, however, lacks a built-in equivalent.

Custom Implementation

Certain approaches involve manually constructing the joined string using a loop and a StringBuilder. While this method offers flexibility, it may be inefficient for large collections.

Java 8 Solution

With the introduction of Java 8, a more elegant and efficient solution emerged: String.join(). This method allows you to directly join a collection of Strings using a specified delimiter:

List<string> list = Arrays.asList("foo", "bar", "baz");
String joined = String.join(" and ", list); // "foo and bar and baz"</string>

Collectors.joining

For non-String collections, the Stream API can be utilized along with the joining Collector:

List<person> list = Arrays.asList(
  new Person("John", "Smith"),
  new Person("Anna", "Martinez"),
  new Person("Paul", "Watson ")
);

String joinedFirstNames = list.stream()
  .map(Person::getFirstName)
  .collect(Collectors.joining(", ")); // "John, Anna, Paul"</person>

StringJoiner

The StringJoiner class provides additional control over the joining process, such as specifying a prefix and suffix for the resulting string:

StringJoiner sj = new StringJoiner(", ", "[", "]");
for (String s : list) {
  sj.add(s);
}

String joined = sj.toString(); // "[foo, bar, baz]"

By incorporating these methods into your Java toolkit, you can efficiently join elements from lists or other collections, ensuring seamless string concatenation operations.

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