Java Eight Filter + Flow Code Representative

In the final dyad of Java 8 tutorials, you lot convey learned how to utilization map(), flatMap(), too other current methods to acquire an agreement of how Java 8 Stream too Lambda expressions acquire inwards slow to perform the mass information functioning on Collection classes similar List or Set. In this Java 8 tutorial, I am going to portion how to utilization the filter() method inwards Java 8, or so other primal method of Stream class.  This is the 1 method you lot volition ever endure used because it forms the primal component subdivision of Stream pipeline. If you lot convey seen or so Java 8 code, you lot would convey already seen this method a dyad of time. The filter() method every bit its advert suggests is used to perform filtering based upon or so boolean conditions.  The status is applied to each chemical ingredient of Stream too those who travel yesteryear the status moves to the adjacent phase too those who don't acquire filtered out.

For example,  if you lot convey a current of integral numbers which contains both fifty-fifty too strange numbers so yesteryear using filter method, you lot tin give the sack exercise or so other current of even numbers or strange numbers yesteryear filtering out others.

Though, filter() method is trivial flake of counter-intuitive, I mean, inwards fellowship to exercise a current of fifty-fifty release you lot telephone yell upwards filter( i -> i % 2 == 0) which way you lot exercise filter(isEven()) but, you are truly filtering out strange numbers to exercise a novel current of fifty-fifty numbers, but that's how it works.

I recall select() would convey been a positive too proper advert for this operation, but, nosotros don't convey whatever command over that can't alter that now.

The primal exercise goodness of using filter() method is lazy evaluation i.e. no information comparing is performed unless you lot telephone yell upwards a terminal functioning on current like findFirst() or forEach().

The filter() method only fix or so pointers when you lot get-go telephone yell upwards them on current too alone performs existent filtering when you lot telephone yell upwards the terminal method. You tin give the sack bring together a proficient Java course of teaching like The Complete Java MasterClass to larn to a greater extent than close Stream too lazy evaluation inwards Java 8. It is likewise 1 of the most up-to-date course, latterly updated for Java 11.

How filter method industrial plant inwards Java 8

In fellowship to larn how to utilization the filter() method inwards Java 8, it's of import that you lot likewise know how it works, at to the lowest degree at a high level. Let's encounter an illustration of filter() method to sympathize the lazy evaluation it does.

Suppose nosotros convey a listing of integer numbers too nosotros desire to abide by the get-go release which is divisible yesteryear both 2 too 3, let' encounter how to solve this occupation inwards Java 8.

List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4, 5, 6, 12, 18); Integer lcm = listOfNumbers.stream()                            .filter(i -> i % 2 == 0)                            .filter(i -> i % three == 0)                            .findFirst().get();        

This code is returning the get-go the get-go release which is divisible yesteryear both 2 too 3. Now, let's encounter how this code volition execute. When you lot telephone yell upwards the filter() method nil happens until you lot telephone yell upwards the findFirst().

At this time, Java knows that it only demand to abide by the get-go chemical ingredient which satisfies the touchstone imposed yesteryear the ii chained filter() methods.

The findFirst() inquire the filter() method prior to it inwards the chain of whatever number, the filter doesn't convey whatever tape so it asks the get-go filter() method, which inwards plow so scan the list too provide a release which is divisible yesteryear 2.

At this time, minute filter method checks if this release is divisible yesteryear 3, if aye so it returns that release to findFirst() otherwise it asks or so other release from get-go filter() method.

This procedure continues until a release is constitute which satisfy both filter() methods. Once that release is constitute it presented to findFirst() method. The project of findFirst() is to provide that number.

This is an illustration of lazy evaluation because nil happens until the telephone yell upwards to findFirst() is a method, this likewise presents an chance to halt every bit presently every bit you lot abide by the get-go release which satisfies your criterion.

There is no demand to procedure the entire listing in 1 lawsuit again too again, every bit it happens inwards the instance of iterative eager evaluation.  You tin give the sack read to a greater extent than close Stream Processing too Lazy Evaluation on Pluralsight's Android versions like  LolliPop, KitKat etc.

The get-go illustration only uses 1 filter() method to impress Strings whose length is greater than 10. The minute illustration prints String which contains the missive of the alphabet "e" similar Gingerbread.

The Third examples combine these ii filter methods to exercise a chain of filter methods to impress String whose length is greater than v too starts amongst a missive of the alphabet "G".

By the way, for testing purpose, you lot tin give the sack likewise exercise a current of integers release yesteryear using Stream.of() static manufacturing flora methods every bit shown inwards the next example:

You tin give the sack encounter that the input current contains numbers from 1 to v but the output current only contains strange numbers. This way fifty-fifty numbers were filtered out because they didn't satisfy the boolean status specified yesteryear Predicate.

I hateful for fifty-fifty release x%2 == 0 too nosotros are checking for x%2 !=0 so they didn't travel yesteryear the status too therefore non progressed to the output stream. If you lot demand to a greater extent than examples, I advise you lot cheque out the Java Streams API Developer Guide yesteryear Nelson Djalo, 1 of the hands-on course of teaching on learning Stream examples live.

How to utilization filter() method inwards Java 8

Here is a sample Java programme to demonstrate how to utilization the filter() method of Stream course of teaching to filter elements from a List or Stream, based upon or so conditions, specified yesteryear Predicate functional interface of Java 8.

package test;  import java.util.ArrayList; import java.util.Arrays; import java.util.List;  /**  * Java 8 filter example. You tin give the sack utilization filter() method to perform lazy filtering  * inwards Java.  */ public class Java8FilterExample {      public static void main(String[] args) {          List<String> versions = new ArrayList<>();         versions.add("Lollipop");         versions.add("KitKat");         versions.add("Jelly Bean");         versions.add("Ice Cream Sandwidth");         versions.add("Honeycomb");         versions.add("Gingerbread");          // Using 1 filter()          // impress all versions whose length is greater than 10 character         System.out.println("All versions whose length greater than 10");         versions.stream()                 .filter(s -> s.length() > 10)                 .forEach(System.out::println);          System.out.println("first chemical ingredient which has missive of the alphabet 'e' ");         String first = versions.stream()                 .filter(s -> s.contains("e"))                 .findFirst().get();         System.out.println(first);                   // Using multiple filter         System.out.println("Element whose length is > v too startswith G");         versions.stream()                 .filter(s -> s.length() > 8)                 .filter(s -> s.startsWith("G"))                 .forEach(System.out::println);                   // or so other illustration of filter() method inwards Java 8         List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4, 5, 6, 12, 18);         Integer lcm = listOfNumbers.stream()                 .filter(i -> i % 2 == 0)                 .filter(i -> i % three == 0)                 .findFirst().get();         System.out.println("first release divisible yesteryear 2 too three inwards the listing is : "                                   + lcm);      }  }  Output All versions whose length greater than 10 Ice Cream Sandwidth Gingerbread first chemical ingredient which has missive of the alphabet 'e'  Jelly Bean Element whose length is > v and starts with G Gingerbread a first release divisible yesteryear 2 and three in the list is : 6

That's all inwards this Java 8 filter() example. It's 1 of the most useful methods of Stream course of teaching too you lot volition abide by yourself using this method fourth dimension too again. The best component subdivision of this method is that it improves performance yesteryear doing lazy evaluation.

The filter() method only setup dyad of pointers too no information comparing is performed until a terminal method e.g. forEach() or findFirst() is called.

You tin give the sack encounter the Java documentation of filter() method to larn to a greater extent than close it, you lot tin give the sack likewise read cheque out the next resources to larn to a greater extent than close Stream too other major enhancements made inwards Java 8.

Further Learning
The Complete Java MasterClass
Java SE 8 for Really Impatient
courses)

20 Example of Date too Time API inwards Java 8 (click here)

10 Examples of Lambda Expression inwards Java 8 (click here)

5 Books to Learn Java 8 Better? (read here)

10 Examples of converting a List to Map inwards Java 8 (see here)

Difference betwixt Stream.map() too Stream.flatMap() inwards Java 8? (answer)

Java 8 Comparator Example (check here)

Collection of best Java 8 tutorials (click here)

10 Examples of Stream inwards Java 8 (example)

Difference betwixt abstract course of teaching too interface inwards Java 8? (answer)

10 Free Courses for Experienced Java Programmers (courses)

How to variety the may yesteryear values inwards Java 8? (example)

How to format/parse the engagement amongst LocalDateTime inwards Java 8? (tutorial)

Top v Course to master copy Java 8 Programming (courses)

Java 8 Interview Questions too Answers (questions)

Thanks for reading this article so far. If you lot similar this Java 8 filter method tutorial so delight portion amongst your friends too colleagues. If you lot convey whatever questions or feedback so delight driblet a note.


P.S.: If you lot only desire to larn to a greater extent than close novel features inwards Java 8 so delight encounter the course What's New inwards Java 8. It explains all the of import features of Java 8 e.g. lambda expressions, streams, functional interfaces, Optional, novel Date Time API too other miscellaneous changes.