Reference to a Constructor (Method References)

Reference to a Constructor

Constructor references are specialized forms of method references that refer to the constructors of a class. They can be created using the className and the keyword new.

Syntax

ClassName::new

Example

Let us write a simple example that contains four files.

Let's assume we have a class called Person that takes a String argument in its constructor to set the name of the person. We can create a method reference to this constructor using the following syntax:

Person::new

This creates a reference to the constructor of the Person class that takes a String argument. We can then use this constructor reference to create new Person objects by passing the String argument to the constructor reference.

For example, let's say we have a list of names and want to create a list of Person objects with those names. We can use the map method of the Stream class along with the Person::new constructor reference like this:

public class Person {
  private final String name;

  public Person(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  @Override
  public String toString() {
    return name;
  }
}

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class ReferenceToConstructor {
  public static void main(String[] args) {
    List<String> names = Arrays.asList("Alice", "Bob", "Charlie");

    List<Person> people =
        names // collection of names stored in list
            .stream() // stream of names
            .map(Person::new) // calling the constructor
            .collect(Collectors.toList());

    System.out.println(people);
  }
}

In this example, we use the map method to apply the Person::new constructor reference to each name in the names list. We pass the name as an argument to the constructor reference to create a new Person object with that name. Finally, we collect the Person objects into a new list using the toList or .collect(Collectors.toList()) method. The output of this program will be:

[Alice, Bob, Charlie]