Java Eight Foreach() Loop Example

Java 8 has introduced a novel way to loop over a List or Collection, past times using the forEach() method of the novel Stream class. You tin sack iterate over whatsoever Collection e.g. List, Set or Map past times converting them into a java.util.sttream.Stream instance together with so calling forEach() method. This method performs given functioning on every chemical gene of Stream, which tin sack last either merely printing it or doing something else. Since flow tin sack last sequential or parallel, the behaviour of if this method is non deterministic if used alongside a parallel stream. One to a greater extent than matter to retrieve most the forEach() method is that it's a terminal operation, which agency yous cannot reuse the Stream after calling this method. It volition throw IllegalStateException if yous attempt to telephone holler upwards some other method on this Stream.

Btw, yous tin sack every bit good telephone holler upwards forEach() method without obtaining Stream from list e.g. listOfString.forEach(), because the forEach() method is every bit good defined inwards Iterable interface, but obtaining Stream gives yous to a greater extent than choices e.g. filtering, mapping or flattening etc.

In this article, yous volition larn how to loop over an ArrayList using the forEach() method of Java 8. It's ane of the many Java 8 tutorials I am going to write this year. If yous are Java developer alongside some years of experience, pass some fourth dimension learning novel features of Java 8, it's going to last ane of the most sought after unloosen inwards coming years.

How to job forEach() method to loop over List inwards Java

In this section, I volition become over a duet of mutual scenarios every Java developer human face upwards inwards their twenty-four hr menses job. In the starting fourth dimension example, nosotros receive got a listing of prime numbers together with nosotros desire to impress it using this novel way of looping inwards Java 8:

List<Integer> listOfPrimes = Arrays.asList(2, 3, 5, 7, 11, 3, 17);          listOfPrimes.stream().forEach((i) -> { System.out.println(i); });

Here nosotros are going through each chemical gene of the flow which is an Integer variable together with passing it to System.out.println() for printing. Since forEach() method accepts a Consumer type, which is a functional interface together with that's why nosotros tin sack top a lambda expression to it.

You tin sack fifty-fifty shorten it past times using method reference, every bit shown below:

listOfPrimes.stream().forEach(System.out::println);

You tin sack job method reference inwards house of the lambda aspect if yous are non doing anything alongside the parameter, except passing it to some other method. For example, inwards our side past times side 2 examples, nosotros cannot supervene upon lambda aspect alongside method reference because nosotros are modifying the element.

You tin sack every bit good come across Java SE 8 for Really Impatient to larn to a greater extent than most method reference together with lambda expression, ane of the amend books to larn Java.

You tin sack fifty-fifty apply other useful flow methods earlier calling forEach() e.g. inwards next code nosotros are using filter() method to alone impress fifty-fifty numbers from the listing of primes:

listOfPrimes.stream().filter(i -> i%2 == 0).forEach(System.out::println);

filter() method from Stream shape await a Predicate instance which is every bit good a functional interface, alongside exactly ane method which returns boolean type, thence yous tin sack job a lambda aspect which returns boolean inwards house of Predicate.

Java 8 forEach example

You tin sack write to a greater extent than code past times next above techniques, I propose yous experiment alongside unlike flow methods to larn more.  Here is my sample programme to demonstrate how to job forEach() disceptation to iterate over every chemical gene of a list, gear upwards or flow inwards Java.

import java.util.Arrays; import java.util.List;  /**  *  Java 8 forEach instance to loop over Stream obtained from a List  *  * @author Javin  */ public class forEachDemo{      public static void main(String args[]) {          List<Integer> listOfPrimes = Arrays.asList(2, 3, 5, 7, 11, 3, 17);          // forEach instance to impress each chemical gene of list         // inwards this instance nosotros are using method reference becasue         // nosotros are non doing anything alongside each chemical gene of collection         // together with exactly passing ito println method         System.out.println("Printing elements of listing using forEach method : ");         listOfPrimes.stream().forEach(System.out::println);                     // let's produce something to each chemical gene earlier printing         // nosotros volition add together comma after each element         System.out.println("Printing elements after adding comma: ");         listOfPrimes.stream().forEach( i -> System.out.print( i + ","));                     // yous tin sack every bit good job forEach alongside parallel stream         // club volition non last guaranteed         System.out.println("\nPrinting elements of listing using parallel stream: ");         listOfPrimes.parallelStream().forEach( i-> System.out.println(i*2));             }  }  Output : run: Printing elements of listing using forEach method: 2 3 5 7 11 3 17 Printing elements after adding comma: 2,3,5,7,11,3,17, Printing elements of listing using parallel stream: 22 14 4 6 34 6 10

You tin sack come across from the output that forEach() disceptation plant exactly similar for loop but it is much to a greater extent than powerful merely because yous tin sack perform the looping inwards parallel without writing a unmarried describe of multi-threading code.

Here is the some other forEach() method defined inwards the Iterable interface, yous tin sack job it straight without calling the stream() method because List, Set or Queue implements Collection together with Iterable interface.

Advantages of forEach() over for loop inwards Java 8 

There are several advantages of using forEach() disceptation over traditional for loop inwards Java 8 e.g.

• More succinct code, sometimes exactly ane liner
• You tin sack top lambda expression, which gives yous the immense flexibility to change what yous produce inwards the loop.
• forEach looping tin sack last made parallel alongside minimal attempt e.g. without writing a unmarried describe of concurrent code, all yous remove to produce is telephone holler upwards parallelStream() method. 

Important points most forEach method

1. forEach() method is defined at 2 places, on Iterable interface every bit good every bit on Stream class. which agency list.forEach() together with list.stream.forEach() both are valid.
2. Prefer using forEach() alongside streams because streams are lazy together with non evaluated until a concluding functioning is called. 
3. forEach() is a concluding operation, yous cannot telephone holler upwards whatsoever method on flow after this.
4. When yous run forEach() method on parallel flow the club on which elements are processed is non guaranteed, though yous tin sack job forEachOrdered() to impose ordering.
5. forEach() method accepts a Consumer instance, which is a functional interface, that's why yous tin sack top a lambda aspect to it. 

That's all most how to job forEach() method to loop over Stream inwards Java. You tin sack job this technique to become over whatsoever Collection, List, Set or Queue inwards Java. They all allow yous to acquire a Stream together with afterwards telephone holler upwards the forEach() method on it. Remember, though, forEach() is a concluding functioning together with yous cannot telephone holler upwards some other method after this. Don't re-use or top approximately streams after calling whatsoever concluding functioning on it e.g. forEach().


Further Learning
The Complete Java MasterClass
tutorial)

How to job Stream shape inwards Java 8 (tutorial)

How to job filter() method inwards Java 8 (tutorial)

How to job forEach() method inwards Java 8 (example)

How to bring together String inwards Java 8 (example)

How to convert List to Map inwards Java 8 (solution)

How to job peek() method inwards Java 8 (example)

5 Books to Learn Java 8 from Scratch (books)

How to convert flow to array inwards Java 8 (tutorial)

Java 8 Certification FAQ (guide)

Java 8 Mock Exams together with Practice Test (test)

Thanks for reading this article so far. If yous similar this article so delight part alongside your friends together with colleagues. If yous receive got whatsoever question, doubt, or feedback so delight driblet a comment together with I'll attempt to response your question.

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