JAVA EE: How to use the distinct method of Java 8 Stream

Tuesday 3 October 2017

How to use the distinct method of Java 8 Stream | Streams in Java 8

Click here to watch in Youtube :
https://www.youtube.com/watch?v=muIXC2upDak&list=UUhwKlOVR041tngjerWxVccw

Person.java

enum Gender
{
    MALE, FEMALE
}

public class Person implements Comparable<Person>
{
    private String name;
    private String email;
    private Gender gender;
    private int age;

    public Person(String name, String email, Gender gender, int age)
    {
        super();
        this.name = name;
        this.email = email;
        this.gender = gender;
        this.age = age;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getEmail()
    {
        return email;
    }

    public void setEmail(String email)
    {
        this.email = email;
    }

    public Gender getGender()
    {
        return gender;
    }

    public void setGender(Gender gender)
    {
        this.gender = gender;
    }

    public int getAge()
    {
        return age;
    }

    public void setAge(int age)
    {
        this.age = age;
    }

    public int compareTo(Person another)
    {
        return this.age - another.getAge();
    }

    @Override
    public String toString()
    {
        return "Person [name=" + name + ", gender=" + gender + ", age=" + age
                + "]";
    }

}

StreamDistinctDemo1.java

import java.util.ArrayList;
import java.util.List;

public class StreamDistinctDemo1
{
    public static void main(String[] args)
    {
        List<Person> personList = new ArrayList<>();

        personList.add(new Person("Alice", "alice@gmail.com", Gender.FEMALE, 15));
        personList.add(new Person("Bob", "bob@gmail.com", Gender.MALE, 15));
        personList.add(new Person("Carol", "carol@gmail.com", Gender.FEMALE, 23));
        personList.add(new Person("David", "david@gmail.com", Gender.MALE, 19));
        personList.add(new Person("Eric", "eric@gmail.com", Gender.MALE, 15));

        /*
         * The distinct() operation returns a stream consisting of the distinct
         * elements (no duplicates) by comparing objects via their equals()
         * method.
         * 
         * Combining with the map and sorted operations, the following code
         * shows distinct age of the persons in the above list, and sorts them
         * in asc order:
         * 
         */
        personList.stream().mapToInt(p -> p.getAge()).distinct().sorted()
                .forEach(System.out::println);
    }

}

Output

15
19
23

StreamDistinctDemo2.java

import java.util.Arrays;

public class StreamDistinctDemo2
{
    public static void main(String[] args)
    {
        int[] numberArray = { 10, 10, 20, 20, 20 };

        /*
         * The following code returns a stream of distinct numbers from an
         * array source
         */
        Arrays.stream(numberArray).distinct()
                .forEach(i -> System.out.print(i + " "));
    }

}