Java - Use Functional Interfaces to code logics

Introduction

Gender enum contains two constants to represent the gender of a person.

Person class represents a person; it contains, apart from other methods, a getPersons() method that returns a list of persons.

The program does the following tasks:

gets a list of persons,
applies a filter to the list to get a list of only males,
maps persons to the year of their birth, and adds one year to each male's date of birth.

It performs each of these actions using lambda expressions.

Demo

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;

enum Gender {//ww  w  .  ja  va2  s. c  o  m
  MALE, FEMALE
}

class Person {
  private String firstName;
  private String lastName;
  private LocalDate dob;
  private Gender gender;

  public Person(String firstName, String lastName, LocalDate dob, Gender gender) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.dob = dob;
    this.gender = gender;
  }

  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 LocalDate getDob() {
    return dob;
  }

  public void setDob(LocalDate dob) {
    this.dob = dob;
  }

  public Gender getGender() {
    return gender;
  }

  public void setGender(Gender gender) {
    this.gender = gender;
  }

  @Override
  public String toString() {
    return firstName + " " + lastName + ", " + gender + ", " + dob;
  }

  // A utility method
  public static List<Person> getPersons() {
    ArrayList<Person> list = new ArrayList<>();
    list.add(new Person("A", "D", LocalDate.of(1975, 1, 20), Gender.MALE));
    list.add(new Person("B", "E", LocalDate.of(1965, 9, 12), Gender.MALE));
    list.add(new Person("C", "D", LocalDate.of(1970, 9, 12), Gender.FEMALE));
    return list;
  }
}

class FunctionUtil {
  // Applies an action on each item in a list
  public static <T> void forEach(List<T> list, Consumer<? super T> action) {
    for (T item : list) {
      action.accept(item);
    }
  }

  // Applies a filter to a list and returned the filtered list items
  public static <T> List<T> filter(List<T> list, Predicate<? super T> predicate) {
    List<T> filteredList = new ArrayList<>();
    for (T item : list) {
      if (predicate.test(item)) {
        filteredList.add(item);
      }
    }
    return filteredList;
  }

  // Maps each item in a list to a value
  public static <T, R> List<R> map(List<T> list, Function<? super T, R> mapper) {
    List<R> mappedList = new ArrayList<>();
    for (T item : list) {
      mappedList.add(mapper.apply(item));

    }
    return mappedList;
  }
}

public class Main {
  public static void main(String[] args) {
    List<Person> list = Person.getPersons();

    // Use the forEach() method to print each person in the list
    System.out.println("Original list of persons:");
    FunctionUtil.forEach(list, p -> System.out.println(p));

    // Filter only males
    List<Person> maleList = FunctionUtil.filter(list, p -> p.getGender() == Gender.MALE);

    System.out.println("\nMales only:");
    FunctionUtil.forEach(maleList, p -> System.out.println(p));

    // Map each person to his/her year of birth
    List<Integer> dobYearList = FunctionUtil.map(list, p -> p.getDob().getYear());

    System.out.println("\nPersons mapped to year of their birth:");
    FunctionUtil.forEach(dobYearList, year -> System.out.println(year));

    // Apply an action to each person in the list
    // Add one year to each male's dob
    FunctionUtil.forEach(maleList, p -> p.setDob(p.getDob().plusYears(1)));

    System.out.println("\nMales only after ading 1 year to DOB:");
    FunctionUtil.forEach(maleList, p -> System.out.println(p));
  }
}

Java - Use Functional Interfaces to code logics

Introduction

Demo

Result

Related Topic