Java 8 Stream API – distinct(), count() & sorted() Example

YatinOctober 1st, 2021Last Updated: December 17th, 2021

0 2,224 4 minutes read

Hello. In this tutorial, we will explore the Stream API methods: sorted(), count(), and distinct() methods introduced in Java 8.

1. Introduction

Before diving deep into the practice stuff let us understand the methods we will be covering in this tutorial.

The distinct() method returns a stream of unique elements. It is a stateful intermediate operation and returns a new stream. This method uses hashCode() and equals() to get the unique elements
The sorted() method returns a stream consisting of elements in the sorted natural order. This method can also accept a comparator to provide customized sorting. It is a stateful intermediate operation and returns a new stream
The count() method returns the count of elements in a stream

2. Practice

Let us dive into some practice stuff from here and I am assuming that you already have the Java 1.8 or greater installed in your local machine. I am using JetBrains IntelliJ IDEA as my preferred IDE. You’re free to choose the IDE of your choice.

2.1 Model class

Create a java file in the com.java8.util package and add the following code. The class will act as a model class for the creation of the employee list.

Employee.java

package com.java8.util;
 
import java.util.ArrayList;
import java.util.List;
 
public class Employee {
    private final String email;
    private final int age;
 
    private Employee(String email, int age) {
        this.email = email;
        this.age = age;
    }
 
    public static List<Employee> create() {
        List<Employee> employees = new ArrayList<>();
        employees.add(new Employee("john@email.com", 21));
        employees.add(new Employee("martin@email.com", 19));
        employees.add(new Employee("marry@email.com", 31));
        employees.add(new Employee("john@email.com", 27));
        employees.add(new Employee("marry@email.com", 25));
 
        return employees;
    }
 
    public String getEmail() {
        return email;
    }
 
    public int getAge() {
        return age;
    }
 
    @Override
    public String toString() {
        return "Employee [email=" + email + ", age=" + age + "]";
    }
}

2.2 Understanding distinct() method

Create a java file in the com.java8 package and add the following code. The class will show the distinct() method implementation in different ways.

DistinctDemo.java

package com.java8;
 
import com.java8.util.Employee;
 
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
 
public class DistinctDemo {
 
    // distinct() method returns a stream of unique elements
    // uses the hashCode() and equals() method to get the unique elements
 
    // removing duplicates from primitive type
    private static void method1() {
        List<Integer> duplicates = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);
        print("Original list: ", duplicates);
 
        List<Integer> unique = duplicates.stream()
                .distinct()
                .collect(Collectors.toList());
        print("Distinct list: ", unique);
    }
 
 
    // removing duplicates from object
    private static void method2() {
        List<Employee> employees = Employee.create();
        print("Original list: ", employees);
 
        List<Employee> distinct = employees.stream()
                .filter(distinctByKey(Employee::getEmail))    // using the predicate to remove the duplicated
                .collect(Collectors.toList());
        print("Distinct list: ", distinct);
    }
 
    // predicate to filter the duplicates by the given key extractor
    // does the job to remove the duplicates
    private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
        Set<Object> seen = ConcurrentHashMap.newKeySet();
        return t -> seen.add(keyExtractor.apply(t));
    }
 
    // print the list
    private static void print(String message, List<?> some) {
        System.out.println(message + some);
    }
 
    // driver code
    public static void main(String[] args) {
        System.out.println("-- Streams distinct() method --\n");
 
        method1();
 
        System.out.println("\n");
 
        method2();
    }
}

Run the file as a java application and if everything goes well the following output will be logged in the IDE console.

Console output

-- Streams distinct() method --
 
Original list: [1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10]
Distinct list: [1, 2, 3, 4, 5, 6, 8, 0, 10]
 
 
Original list: [Employee [email=john@email.com, age=21], Employee [email=martin@email.com, age=19], Employee [email=marry@email.com, age=31], Employee [email=john@email.com, age=27], Employee [email=marry@email.com, age=25]]
Distinct list: [Employee [email=john@email.com, age=21], Employee [email=martin@email.com, age=19], Employee [email=marry@email.com, age=31]]

2.3 Understanding count() method

Create a java file in the com.java8 package and add the following code. The class will show the count() method implementation in different ways.

CountDemo.java

package com.java8;
 
import com.java8.util.Employee;
 
import java.util.Arrays;
import java.util.List;
 
public class CountDemo {
 
    // count() method counts the number of elements in the stream
 
    private static void method1() {
        List<Integer> list = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);
 
        long total = list.stream()
                .count();
        System.out.println("Total elements = " + total);
    }
 
    private static void method2() {
        List<Employee> employees = Employee.create();
 
        long total = employees.stream().count();
        System.out.println("Total employees = " + total);
 
        long freshers = employees.stream()
                .filter(employee -> employee.getAge() <= 21)
                .count();
        System.out.println("Total employees after filter(..) op = " + freshers);
    }
 
    // driver code
    public static void main(String[] args) {
        System.out.println("-- Streams count() method --\n");
 
        method1();
 
        System.out.println("\n");
 
        method2();
    }
}

Run the file as a java application and if everything goes well the following output will be logged in the IDE console.

Console output

-- Streams count() method --
 
Total elements = 12
 
Total employees = 5
Total employees after filter(..) op = 2

2.4 Understanding sorted() method

Create a java file in the com.java8 package and add the following code. The class will show the sorted() method implementation in different ways.

SortedDemo.java

package com.java8;
 
import com.java8.util.Employee;
 
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
 
public class SortedDemo {
 
    // sorted() method returns a stream consisting of elements in a sorted order
    // it is a stateful intermediate operation
 
    // sorting primitive type list
    private static void method1() {
        List<Integer> unsorted = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);
        System.out.println("Unsorted stream:" + unsorted);
 
        List<Integer> sorted = unsorted.stream()
                .sorted()
                .collect(Collectors.toList());
        System.out.println("Sorted stream:" + sorted);
    }
 
    // sorting object list
    private static void method2() {
        List<Employee> employees = Employee.create();
 
        List<Employee> sorted = employees.stream()
                .sorted(Comparator.comparing(Employee::getAge))    // sorting the employees by age
                .collect(Collectors.toList());
        System.out.println("Sorted list : " + sorted);
    }
 
    // driver code
    public static void main(String[] args) {
        System.out.println("-- Streams sorted() method --\n");
 
        method1();
 
        System.out.println("\n");
 
        method2();
    }
}

Run the file as a java application and if everything goes well the following output will be logged in the IDE console.

Console output

-- Streams sorted() method --
 
Unsorted stream:[1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10]
Sorted stream:[0, 1, 1, 2, 2, 3, 4, 5, 6, 6, 8, 10]
 
Sorted list : [Employee [email=martin@email.com, age=19], Employee [email=john@email.com, age=21], Employee [email=marry@email.com, age=25], Employee [email=john@email.com, age=27], Employee [email=marry@email.com, age=31]]

That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share!

4. Summary

In this tutorial, we learned the sorted(), count(), and distinct() methods introduced in java8 programming along with the implementation. You can download the source code from the Downloads section.

5. Download the Project

This was a tutorial on learning and implementing the sorted(), count(), and distinct() methods in Java 8.

Download
You can download the full source code of this example here: Java 8 Stream API – distinct(), count() & sorted() Example

Java 8 Stream API – distinct(), count() & sorted() Example

1. Introduction

2. Practice

2.1 Model class

2.2 Understanding distinct() method

2.3 Understanding count() method

Thank you!

2.4 Understanding sorted() method

4. Summary

5. Download the Project

Thank you!

Yatin

Thank you!

1. Introduction

2. Practice

2.1 Model class

2.2 Understanding distinct() method

2.3 Understanding count() method

Thank you!

2.4 Understanding sorted() method

4. Summary

5. Download the Project

Thank you!

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Thank you!