Home  >  Java 8

Parallel and Sequential Stream in Java 8 Collection

By Arvind Rai, April 27, 2014
Java 8 Collection has been enriched by stream methods. These methods are stream() and parallelStream() which are default methods and have been written in Collection interface. So that it will present in all implementing classes. With the help of these methods, we can write the code efficient. Old fashioned large number of line of code can be written in single liner of code. We see Parallel and Sequential Stream one by one with the example.

Parallel Stream

Collection.parallelStream() returns parallel stream instance for calling collection. The Stream object can be used for different purpose. In this example we have taken a list of employee which has salary field. For a given predicate, we will filter the list and then will calculate the average salary. Find the code below.
ParallelStreamDemo.java
package com.concretepage.util.stream;
import java.util.ArrayList;
import java.util.List;
import java.util.OptionalDouble;
import java.util.function.Predicate;
public class ParallelStreamDemo {
    public static void main(String[] args) {
        List<Employee> list = new ArrayList<>();
        list.add(new Employee(1, "A", 2000));
        list.add(new Employee(2, "B", 3000));
        list.add(new Employee(3, "C", 4000));
        list.add(new Employee(4, "D", 5000));

        Predicate<Employee> seniorEmp = e -> e.sal > 3000 && e.sal < 6000;
        OptionalDouble averageSal = list.parallelStream().filter(seniorEmp)
                .mapToDouble(e -> e.sal).average();
				
        System.out.println(averageSal.getAsDouble());
    }
} 
Find the Employee class which is being used as value object.
Employee.java
package com.concretepage.util.stream;
public class Employee {
 public int id;
 public String name;
 public int sal;
 public Employee(int id,String name,int sal  ){
     this.id = id;
     this.name = name;
     this.sal = sal;
 }
} 
Output will be 4500.0


Sequential Stream

Collection.stream() returns a sequential stream instance for calling collection. To understand Sequential stream, I am calculating the sum of salary for a given predicate. Find the example.
SequentialStreamDemo.java
package com.concretepage.util.stream;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
public class SequentialStreamDemo {
    public static void main(String[] args) {
        List<Employee> list = new ArrayList<>();
        list.add(new Employee(1, "A", 2000));
        list.add(new Employee(2, "B", 3000));
        list.add(new Employee(3, "C", 4000));
        list.add(new Employee(4, "D", 5000));

        Predicate<Employee> juniorEmp = e -> e.sal > 1000 && e.sal < 4000;
        int salsum = list.stream().filter(juniorEmp)
                .mapToInt(e -> e.sal).sum();
				
        System.out.println(salsum);
    }
} 
Output will be 5000
POSTED BY
ARVIND RAI
ARVIND RAI
FIND MORE TUTORILAS






©2019 concretepage.com | Privacy Policy | Contact Us