Java - Stream Find Operation

Introduction

The following methods in the Stream interface are used to perform find operations:

Optional<T> findAny()
Optional<T> findFirst()

IntStream, LongStream, and DoubleStream also contain the same methods for primitive types.

All find operations are terminal operations.

They are also short-circuiting operations.

A short-circuiting operation may not have to process the entire stream to return the result.

The return type of the findAny() and findFirst() methods is Optional<T> because these methods may not have a result if the stream is empty.

Demo

import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;

public class Main {
  public static void main(String[] args) {
    // Get the list of persons
    List<Person> persons = Person.persons();

    // Find any male
    Optional<Person> anyMale = persons.stream().filter(Person::isMale).findAny();

    if (anyMale.isPresent()) {
      System.out.println("Any male: " + anyMale.get());
    } else {/*w  w  w  .  j  av  a2 s  . c  om*/
      System.out.println("No male found.");
    }

    // Find the first male
    Optional<Person> firstMale = persons.stream().filter(Person::isMale).findFirst();
    if (firstMale.isPresent()) {
      System.out.println("First male: " + anyMale.get());
    } else {
      System.out.println("No male found.");
    }
  }
}

class Person {
  // An enum to represent the gender of a person
  public static enum Gender {
    MALE, FEMALE
  }

  private long id;
  private String name;
  private Gender gender;
  private LocalDate dob;
  private double income;

  public Person(long id, String name, Gender gender, LocalDate dob, double income) {
    this.id = id;
    this.name = name;
    this.gender = gender;
    this.dob = dob;
    this.income = income;
  }

  public long getId() {
    return id;
  }

  public void setId(long id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public Gender getGender() {
    return gender;
  }

  public boolean isMale() {
    return this.gender == Gender.MALE;
  }

  public boolean isFemale() {
    return this.gender == Gender.FEMALE;
  }

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

  public LocalDate getDob() {
    return dob;
  }

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

  public double getIncome() {
    return income;
  }

  public void setIncome(double income) {
    this.income = income;
  }

  public static List<Person> persons() {
    Person ken = new Person(1, "Java", Gender.MALE, LocalDate.of(1970, Month.MAY, 4), 6020.0);
    Person jeff = new Person(2, "Jack", Gender.MALE, LocalDate.of(1970, Month.JULY, 15), 7320.0);
    Person donna = new Person(3, "Javascript", Gender.FEMALE, LocalDate.of(1972, Month.JULY, 29), 8720.0);
    Person chris = new Person(4, "XML", Gender.MALE, LocalDate.of(1993, Month.DECEMBER, 16), 5800.0);
    Person laynie = new Person(5, "Json", Gender.FEMALE, LocalDate.of(2002, Month.DECEMBER, 13), 0.0);
    Person lee = new Person(6, "Database", Gender.MALE, LocalDate.of(2011, Month.MAY, 9), 2400.0);

    // Create a list of persons
    List<Person> persons = Arrays.asList(ken, jeff, donna, chris, laynie, lee);

    return persons;
  }

  @Override
  public String toString() {
    String str = String.format("(%s, %s, %s, %s, %.2f)", id, name, gender, dob, income);
    return str;
  }
}

Result