Streams ForEach
Description
The forEach operation takes an action for each element of the stream.
The Stream<T> interface contains two methods to perform the forEach operation:
void forEach(Consumer<? super T> action)
void forEachOrdered(Consumer<? super T> action)
IntStream, LongStream, and DoubleStream contain the same methods.
The forEach() method does not guarantee the order in which the action for each element in the stream is applied.
The forEachOrdered() method performs the action in the order of elements defined by the stream.
forEachOrdered() method may slow down processing in a parallel stream.
Example
The following code prints the details of females in the employee list:
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;
/*from w w w.j av a2s. c o m*/
public class Main {
public static void main(String[] args) {
Employee.persons()
.stream()
.filter(Employee::isFemale)
.forEach(System.out::println);
}
}
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 isFemale() {
return this.gender == Gender.FEMALE;
}
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.
Example 2
The following code shows how to use the forEach() method to increase the income of all females by 10%.
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;
/*from w w w . j av a 2s . com*/
public class Main {
public static void main(String[] args) {
List<Employee> persons = Employee.persons();
System.out.println("Before increasing the income: " + persons);
persons.stream()
.filter(Employee::isFemale)
.forEach(p -> p.setIncome(p.getIncome() * 1.10));
System.out.println("After increasing the income: " + persons);
}
}
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 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 double getIncome() {
return income;
}
public void setIncome(double income) {
this.income = income;
}
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;
}
@Override
public String toString() {
String str = String.format("(%s, %s, %s, %s, %.2f)\n", id, name, gender,
dob, income);
return str;
}
}
The code above generates the following result.
