Examples using constructors using Java

Main.java

class Person {

    private String lastName;
    private String firstName;

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

    public Person(String firstName, String lastName) {
        this(firstName);
        this.lastName = lastName;
    }

    public String greet() {

        if (firstName != null && lastName != null) {
            return "Hello, " + firstName + " " + lastName;
        }
        return "Hello, " + firstName;
    }

    public String getFirstName() {
        return firstName;
    }

    @Override
    public String toString() {
        if (firstName != null && lastName != null) {
            return firstName + " " + lastName;
        };
        return firstName;
    }
}

class Couple {
    Person guy;
    Person girl;

    public Couple(Person guy, Person girl) {
        this.guy = guy;
        this.girl = girl;
    }

    @Override
    public String toString() {
        return guy + " is dating " + girl;
    }
}

public class Main {

    public static void main(String[] args) {

        Person yegan = new Person("Yegan", "James");
        Person alice = new Person("Alice", "Jansseune");

        System.out.println(yegan.greet());
        System.out.println(alice.greet());

        Couple yeganAndAlice = new Couple(yegan, alice);
        System.out.println(yeganAndAlice);

    }
}