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
Highly recommend this Streams tutorial – Processing Data with Java SE 8 Streams
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; }This should be
if (!filter.equals(line)) {
Dear Mkyong,
Thanks for your post, it is very helpful.
i wondering that, this tutorial,
findAny() -> in the for each, the result will always find the last matched item in the list, but in the stream(). filter -> the result will do random; because the stream will not process the result as order;
I think the result will be diffence with the list includes multiple values mathe with codition in the filtering in the list.
Nice post. Can you please add example where we can use ternary operator inside stream filter.
Great…….thanks 😉
Great !!!!!!
Great!!!! Thanks
Hi, Could you check the method getFilterOutput ? you have an unused parameter
A tutorial in Java 8 that returns null. Not cool.
Hi mkyong,
Your tutorials are great. What about starting a blog on minds.com?
The times of Facebook and Twitter are coming to an end …
Regards
Claus
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);
i think you can do this .filter(p-> {“jack”.equals(p.getName()) && 20==p.getAge()});
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.
Thank you
It is very useful
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.
it depends on how you’re comparing it. Sequential streams? Parallel streams? Streams are NOT always slower than loops. Yes, streams are sometimes slower than loops, but they can also be equally fast; it depends on the circumstances.
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.
Hi,
how can i filter String only by char? i.g. i want to remove some char from a String?
you can sue String.chars to get it
Better way to manipulate with Strings is regular expressions. IMHO.
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?
thanks for sharing
Thanks a lot! This was so helpful!
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.
How would I filter the last (n) elements added to list using streams?
In your first example shouldn’t you be using !filter.equals(line)?
Yes
List result = lines.stream()
.filter(line -> !filter.equals(line))
.collect(Collectors.toList());
yes i think too
Love you mkyong. Great Job. Requesting you to please do the same job for spring boot and other modules like Spring Cloud etc..
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!!!!
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.