Streams support a count operation through the count() method.
The following code prints the number of elements in the stream of people:
long personCount = Person.persons()
.stream()
.count();
import java.time.LocalDate; import java.time.Month; import java.util.Arrays; import java.util.List; import java.util.OptionalDouble; public class Main { public static void main(String[] args) { long personCount = Person.persons() .stream()/* w w w. j a va 2s. co m*/ .count(); System.out.println(personCount); } } 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; } }