Streams Find
Description
The Streams API supports different types of find operations on stream elements.
The following methods in the Stream interface are used to perform find operations:
Optional<T> findAny()
Optional<T> findFirst()
The primitive type streams such as IntStream, LongStream, and DoubleStream also contain the same methods that work with a predicate and an optional one 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.
Example
The following code shows how to perform find operations on streams.
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
/* ww w . jav a2s .com*/
public class Main {
public static void main(String[] args) {
List<Employee> persons = Employee.persons();
// Find any male
Optional<Employee> anyMale = persons.stream().filter(Employee::isMale).findAny();
if (anyMale.isPresent()) {
System.out.println("Any male: " + anyMale.get());
} else {
System.out.println("No male found.");
}
// Find the first male
Optional<Employee> firstMale = persons.stream().filter(Employee::isMale).findFirst();
if (firstMale.isPresent()) {
System.out.println("First male: " + anyMale.get());
} else {
System.out.println("No male found.");
}
}
}
class Employee {
public static enum Gender {
MALE, FEMALE
}
private long id;
private String name;
private Gender gender;
private LocalDate dob;
private double income;
public Employee(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 boolean isMale() {
return this.gender == Gender.MALE;
}
public static List<Employee> persons() {
Employee p1 = new Employee(1, "Jake", Gender.MALE, LocalDate.of(1971,
Month.JANUARY, 1), 2343.0);
Employee p2 = new Employee(2, "Jack", Gender.MALE, LocalDate.of(1972,
Month.JULY, 21), 7100.0);
Employee p3 = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1973,
Month.MAY, 29), 5455.0);
Employee p4 = new Employee(4, "Jode", Gender.MALE, LocalDate.of(1974,
Month.OCTOBER, 16), 1800.0);
Employee p5 = new Employee(5, "Jeny", Gender.FEMALE, LocalDate.of(1975,
Month.DECEMBER, 13), 1234.0);
Employee p6 = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1976,
Month.JUNE, 9), 3211.0);
List<Employee> persons = Arrays.asList(p1, p2, p3, p4, p5, p6);
return persons;
}
}
The code above generates the following result.
