Collectors summarizingLong(ToLongFunction<? super T> mapper)
returns a Collector which applies an long-producing mapping function, and returns summary statistics for the resulting values.
summarizingLong
has the following syntax.
public static <T> Collector<T,?,LongSummaryStatistics> summarizingLong(ToLongFunction<? super T> mapper)
The following example shows how to use summarizingLong
.
import java.time.LocalDate; import java.time.Month; import java.util.Arrays; import java.util.List; import java.util.LongSummaryStatistics; import java.util.stream.Collectors; //from w w w . j a va 2s . c o m public class Main { public static void main(String[] args) { LongSummaryStatistics incomeStats = Employee.persons() .stream() .collect(Collectors.summarizingLong(Employee::getIncome)); System.out.println(incomeStats); } } class Employee { public static enum Gender { MALE, FEMALE } private long id; private String name; private Gender gender; private LocalDate dob; private long income; public Employee(long id, String name, Gender gender, LocalDate dob, long income) { this.id = id; this.name = name; this.gender = gender; this.dob = dob; this.income = income; } public long getIncome() { return income; } public static List<Employee> persons() { Employee p1 = new Employee(1, "Jake", Gender.MALE, LocalDate.of(1971, Month.JANUARY, 1), 2343); Employee p2 = new Employee(2, "Jack", Gender.MALE, LocalDate.of(1972, Month.JULY, 21), 7100); Employee p3 = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1973, Month.MAY, 29), 5455); Employee p4 = new Employee(4, "Jode", Gender.MALE, LocalDate.of(1974, Month.OCTOBER, 16), 1800); Employee p5 = new Employee(5, "Jeny", Gender.FEMALE, LocalDate.of(1975, Month.DECEMBER, 13), 1234); Employee p6 = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1976, Month.JUNE, 9), 3211); List<Employee> persons = Arrays.asList(p1, p2, p3, p4, p5, p6); return persons; } }
The code above generates the following result.