Java 8 Streams filter examples

In this tutorial, we will show you few Java 8 examples to demonstrate the use of Streams filter(), collect(), findAny() and orElse()

1. Streams filter() and collect()

1.1 Before Java 8, filter a List like this :

BeforeJava8.java

package com.mkyong.java8;

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

public class BeforeJava8 {

    public static void main(String[] args) {

        List<String> lines = Arrays.asList("spring", "node", "mkyong");
        List<String> result = getFilterOutput(lines, "mkyong");
        for (String temp : result) {
            System.out.println(temp);    //output : spring, node
        }

    }

    private static List<String> getFilterOutput(List<String> lines, String filter) {
        List<String> result = new ArrayList<>();
        for (String line : lines) {
            if (!"mkyong".equals(line)) { // we dont like mkyong
                result.add(line);
            }
        }
        return result;
    }

}

Output


spring
node

1.2 The equivalent example in Java 8, stream.filter() to filter a List, and collect() to convert a stream into a List.

NowJava8.java

package com.mkyong.java8;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class NowJava8 {

    public static void main(String[] args) {

        List<String> lines = Arrays.asList("spring", "node", "mkyong");

        List<String> result = lines.stream()                // convert list to stream
                .filter(line -> !"mkyong".equals(line))     // we dont like mkyong
                .collect(Collectors.toList());              // collect the output and convert streams to a List

        result.forEach(System.out::println);                //output : spring, node

    }

}

Output


spring
node

2. Streams filter(), findAny() and orElse()

Person.java

package com.mkyong.java8;

public class Person {

    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    //gettersm setters, toString
}

2.1 Before Java 8, you get a Person by name like this :

BeforeJava8.java

package com.mkyong.java8;

import java.util.Arrays;
import java.util.List;

public class BeforeJava8 {

    public static void main(String[] args) {

        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );

        Person result = getStudentByName(persons, "jack");
        System.out.println(result);

    }

    private static Person getStudentByName(List<Person> persons, String name) {

        Person result = null;
        for (Person temp : persons) {
            if (name.equals(temp.getName())) {
                result = temp;
            }
        }
        return result;
    }
}

Output


Person{name='jack', age=20}

2.2 The equivalent example in Java 8, use stream.filter() to filter a List, and .findAny().orElse (null) to return an object conditional.

NowJava8.java

package com.mkyong.java8;

import java.util.Arrays;
import java.util.List;

public class NowJava8 {

    public static void main(String[] args) {

        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );

        Person result1 = persons.stream()                        // Convert to steam
                .filter(x -> "jack".equals(x.getName()))        // we want "jack" only
                .findAny()                                      // If 'findAny' then return found
                .orElse(null);                                  // If not found, return null

        System.out.println(result1);
        
        Person result2 = persons.stream()
                .filter(x -> "ahmook".equals(x.getName()))
                .findAny()
                .orElse(null);

        System.out.println(result2);

    }

}

Output


Person{name='jack', age=20}
null

2.3 For multiple condition.

NowJava8.java

package com.mkyong.java8;

import java.util.Arrays;
import java.util.List;

public class NowJava8 {

    public static void main(String[] args) {

        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );

        Person result1 = persons.stream()
                .filter((p) -> "jack".equals(p.getName()) && 20 == p.getAge())
                .findAny()
                .orElse(null);

        System.out.println("result 1 :" + result1);

        //or like this
        Person result2 = persons.stream()
                .filter(p -> {
                    if ("jack".equals(p.getName()) && 20 == p.getAge()) {
                        return true;
                    }
                    return false;
                }).findAny()
                .orElse(null);

        System.out.println("result 2 :" + result2);

    }


}

Output


result 1 :Person{name='jack', age=20}
result 2 :Person{name='jack', age=20}

3. Streams filter() and map()

NowJava8.java

package com.mkyong.java8;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class NowJava8 {

    public static void main(String[] args) {

        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );

        String name = persons.stream()
                .filter(x -> "jack".equals(x.getName()))
                .map(Person::getName)                        //convert stream to String
                .findAny()
                .orElse("");

        System.out.println("name : " + name);

        List<String> collect = persons.stream()
                .map(Person::getName)
                .collect(Collectors.toList());

        collect.forEach(System.out::println);

    }
    
}

Output


name : jack

mkyong
jack
lawrence
Note
Highly recommend this Streams tutorial – Processing Data with Java SE 8 Streams

References

  1. Java 8 cyclic inference in my case
  2. Java 8 Explained: Using Filters, Maps, Streams and Foreach to apply Lambdas to Java Collections!
  3. Java 8 forEach examples
  4. Java 8 Streams: multiple filters vs. complex condition
  5. Processing Data with Java SE 8 Streams

About the Author

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mkyong
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

Comments

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Python490
Guest
Python490

In your first example shouldn’t you be using !filter.equals(line)?

Xyz
Guest
Xyz

Yes

Xyz
Guest
Xyz

List result = lines.stream()
.filter(line -> !filter.equals(line))
.collect(Collectors.toList());

Akshay
Guest
Akshay
private static Person getStudentByName(List persons, String name) { Person result = null; for (Person temp : persons) { if (name.equals(temp.getName())) { result = temp; } } return result; } You need to break the loop once you have found the result.
Aditi Patel
Guest
Aditi Patel

Java 8 goes one more step ahead and has developed a Streams API which lets us think about parallelism. Nowadays, because of the tremendous amount of development on the hardware front, multicore CPUs are becoming more and more general.

Great Article. Keep going !!

Can you post the basic interview questions for this topic?

degan
Guest
degan

Thank you
It is very useful

bakcsa83
Guest
bakcsa83

Thanks for posting this nice example. However, everybody should know that stream().filter() 3 times slower than a good old for loop with “manual” filtering on the desired properties.

rahul
Guest
rahul

thanks for sharing

Malipan Bâ
Guest
Malipan Bâ

Hello @Mkyon. Is there possible to multiple filter like this:
Person result1 = persons.stream()
.filter((p) -> “jack”.equals(p.getName())).filter((p)-> 20 == p.getAge()))
.findAny()
.orElse(null);

TKBHL
Guest
TKBHL

These examples as useful as always here. Thanks a lot! But I’m not sure about “.orElse(null)”. Avoiding null to indicate absent of the result is the whole point of Optional, and this is re-introducing the null.

Rock
Guest
Rock

Hi,
how can i filter String only by char? i.g. i want to remove some char from a String?

yang
Guest
yang

you can sue String.chars to get it

Random
Guest
Random

Thanks a lot! This was so helpful!

Jenith
Guest
Jenith

Hi MKYong how to compare a field from two lists of object and it should return the filtered values as list of first list type.

Rob
Guest
Rob

How would I filter the last (n) elements added to list using streams?

Savani
Guest
Savani

Love you mkyong. Great Job. Requesting you to please do the same job for spring boot and other modules like Spring Cloud etc..

Mykola Bova
Guest
Mykola Bova

Thanks a lot!! A question. Regarding parts Streams filter(), findAny() and orElse() What if more than one result will be found? Can we expect a List as result? Thank you!!!!

Mo
Guest
Mo

A little late, but for anyone looking at this later. I believe you can convert the stream to a list using .collect(Collectors.toList()) on the stream.

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