CalculationsExample.java

package com.kiroule.ocpupgradejava8.topic4_4;

import java.util.Arrays;
import java.util.List;
import java.util.OptionalDouble;
import java.util.OptionalInt;

/**
 * @author Igor Baiborodine
 */
public class CalculationsExample {

  public static void main(String... args) {

    List<FuturamaCharacter> characters = Arrays.asList(
        new FuturamaCharacter("Bender", "Rodriguez", 5),
        new FuturamaCharacter("Philip", "Fry", 126),
        new FuturamaCharacter("Turanga", "Leela", 22));

    System.out.println("Futurama characters:");
    characters.forEach(System.out::println); // c -> System.out.println(c)

    long count = characters
        .stream()
        .count();
    System.out.println("\nCharacters count: " + count);

    OptionalInt minAge = characters
        .stream()
        .mapToInt(FuturamaCharacter::getAge) // c -> c.getAge()
        .min();
    System.out.println("Characters min age: "
                       + (minAge.isPresent() ? minAge.getAsInt() : "Not available"));

    OptionalInt maxAge = characters
        .stream()
        .mapToInt(FuturamaCharacter::getAge)
        .max();
    System.out.println("Characters max age: "
                       + (maxAge.isPresent() ? maxAge.getAsInt() : "Not available"));

    OptionalDouble averageAge = characters
        .stream()
        .mapToDouble(FuturamaCharacter::getAge)
        .average();
    System.out.println("Characters average age: "
                       + (averageAge.isPresent() ? averageAge.getAsDouble() : "Not available"));

    int sumAge = characters
        .stream()
        .mapToInt(FuturamaCharacter::getAge)
        .sum();
    System.out.println("Characters sum of ages: " + sumAge);
  }
}

class FuturamaCharacter {

  private String firstName;
  private String lastName;
  private int age = 0;

  public FuturamaCharacter(String firstName, String lastName, int age) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
  }

  public int getAge() {
    return age;
  }

  @Override
  public String toString() {
    return firstName + " " + lastName + " [" + age + "]";
  }
}