Example demonstrating Lambdas in Java

Main.java

package ge.tsu.lambdas;

import java.util.function.Consumer;
import java.util.function.Predicate;

public class Main {

	public static void main(String... args) {
		
		Person kaiKaci = new Person("Nikoloz", "Grdzelidze", 28);
		Person pataraKaci = new Person("Giorgi", "Asatiani", 17);
		Person amuricanMan = new Person("John" ,"Smith", 12);
		
		Amurica amurica = new Amurica();
		Georgia georgia = new Georgia();

		System.out.println("Georgians:");
		System.out.println(kaiKaci);
		System.out.println(pataraKaci);
		
		System.out.println("Amuricans:");
		System.out.println(amuricanMan);
		
		// Check ages
		georgia.tellMeIfMyAgeIsLegal(kaiKaci);
		georgia.tellMeIfMyAgeIsLegal(pataraKaci);
		amurica.tellMeIfMyAgeIsLegal(amuricanMan);
		
		System.out.println();
		
		// Change surnames
		georgia.changeSurnameTo(kaiKaci, "Grdzelishvili");
		georgia.changeSurnameTo(pataraKaci, pataraKaci.getLastname().substring(0, pataraKaci.getLastname().length() - 1).concat("oglu"));
		amurica.changeSurnameTo(amuricanMan, "Brown");
		
		System.out.println("Georgians:");
		System.out.println(kaiKaci);
		System.out.println(pataraKaci);
		
		System.out.println("Amuricans:");
		System.out.println(amuricanMan);
	}
}

class Person {
	private String firstname;
	private String lastname;
	private int age;

	public Person() {
	}

	public Person(String firstname, String lastname, int age) {
		this.firstname = firstname;
		this.lastname = lastname;
		this.age = age;
	}

	public String getFirstname() {
		return firstname;
	}

	public void setFirstname(String firstname) {
		this.firstname = firstname;
	}

	public String getLastname() {
		return lastname;
	}

	public void setLastname(String lastname) {
		this.lastname = lastname;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	@Override
	public String toString() {
		return "Person [firstname=" + firstname + ", lastname=" + lastname + ", age=" + age + "]";
	}
}

interface Countryable {
	
	public abstract void changeSurnameTo(Person person, String newSurname);
	
	public abstract void tellMeIfMyAgeIsLegal(Person person);
}

class Georgia implements Countryable {

	@Override
	public void changeSurnameTo(Person person, String newSurname) {
		Country.changeSurnameWithConsumer(person, c -> c.setLastname(newSurname));
	}
	
	@Override
	public void tellMeIfMyAgeIsLegal(Person person) {
		// Call helper method :)
		Country.printHasLegalAge(person, p -> p.getAge() > 18); // Pass georgian predicate here!
	}
}

class Amurica implements Countryable {

	@Override
	public void changeSurnameTo(Person person, String newSurname) {
		// All Amuricans add middlenames of President Trump :|  
		Country.changeSurnameWithConsumer(person, c -> c.setLastname("J. " + newSurname)); 
	}
	
	@Override
	public void tellMeIfMyAgeIsLegal(Person person) {
		// Every Amurican drinks at any age :| 
		Country.printHasLegalAge(person, p -> {
			return p.getAge() > 0;
		}); 
	}
}

final class Country {
	
	static <T> void changeSurnameWithConsumer(T someone, Consumer<T> surnameChanger) {
		surnameChanger.accept(someone);
	}
	
	static <T> void printHasLegalAge(T someone, Predicate<T> predicate) {
		if (predicate.test(someone)) {
			System.out.println(String.format("%s has legal age. :)", someone));
		} else {
			System.out.println(String.format("%s has illegal age! :(", someone));
		}
	}
}