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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 iterate over whatever Collection e.g. List, Set or Map past times converting them into a java.util.sttream.Stream instance in addition to and so calling forEach() method. This method performs given functioning on every chemical ingredient of Stream, which tin hold upward either exactly printing it or doing something else. Since current tin hold upward sequential or parallel, the behaviour of if this method is non deterministic if used amongst a parallel stream. One to a greater extent than affair to recollect almost the forEach() method is that it's a terminal operation, which way you lot cannot reuse the Stream after calling this method. It volition throw IllegalStateException if you lot attempt to telephone weep upward some other method on this Stream.

Btw, you lot tin too telephone weep upward forEach() method without obtaining Stream from list e.g. listOfString.forEach(), because the forEach() method is too defined inwards Iterable interface, but obtaining Stream gives you lot to a greater extent than choices e.g. filtering, mapping or flattening etc.

In this article, you lot volition larn how to loop over an ArrayList using the forEach() method of Java 8. It's 1 of the many Java 8 tutorials I am going to write this year. If you lot are Java developer amongst some years of experience, pass some fourth dimension learning novel features of Java 8, it's going to hold upward 1 of the most sought after unloose inwards coming years.

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

In this section, I volition acquire over a twain of mutual scenarios every Java developer confront inwards their twenty-four hours job. In the outset example, nosotros receive got a listing of prime numbers in addition to 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 ingredient of the current which is an Integer variable in addition to passing it to System.out.println() for printing. Since forEach() method accepts a Consumer type, which is a functional interface in addition to that's why nosotros tin transcend a lambda expression to it.

You tin fifty-fifty shorten it past times using method reference, equally shown below:

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

You tin utilization method reference inwards house of the lambda appear if you lot are non doing anything amongst the parameter, except passing it to some other method. For example, inwards our adjacent 2 examples, nosotros cannot supplant lambda appear amongst method reference because nosotros are modifying the element.

You tin too run across Java SE 8 for Really Impatient to larn to a greater extent than almost method reference in addition to lambda expression, 1 of the ameliorate books to larn Java.

You tin fifty-fifty apply other useful current methods earlier calling forEach() e.g. inwards next code nosotros are using filter() method to solely 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 appear a Predicate instance which is too a functional interface, amongst exactly 1 method which returns boolean type, therefore you lot tin utilization a lambda appear which returns boolean inwards house of Predicate.

Java 8 forEach example

You tin write to a greater extent than code past times next above techniques, I advise you lot experiment amongst unlike current methods to larn more.  Here is my sample programme to demonstrate how to utilization forEach() arguing to iterate over every chemical ingredient of a list, fix or current inwards Java.

import java.util.Arrays; import java.util.List;  /**  *  Java 8 forEach representative 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 representative to impress each chemical ingredient of list         // inwards this instance nosotros are using method reference becasue         // nosotros are non doing anything amongst each chemical ingredient of collection         // in addition to exactly passing ito println method         System.out.println("Printing elements of listing using forEach method : ");         listOfPrimes.stream().forEach(System.out::println);                     // let's create something to each chemical ingredient 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 + ","));                     // you lot tin too utilization forEach amongst parallel stream         // gild volition non hold upward 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 run across from the output that forEach() arguing industrial plant exactly similar for loop but it is much to a greater extent than powerful exactly because you lot tin perform the looping inwards parallel without writing a unmarried trace of multi-threading code.

Here is the some other forEach() method defined inwards the Iterable interface, you lot tin utilization it straight without calling the stream() method because List, Set or Queue implements Collection in addition to Iterable interface.

Advantages of forEach() over for loop inwards Java 8 

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

• More succinct code, sometimes exactly 1 liner
• You tin transcend lambda expression, which gives you lot the immense flexibility to change what you lot create inwards the loop.
• forEach looping tin hold upward made parallel amongst minimal attempt e.g. without writing a unmarried trace of concurrent code, all you lot postulate to create is telephone weep upward parallelStream() method. 

Important points almost forEach method

1. forEach() method is defined at 2 places, on Iterable interface equally good equally on Stream class. which way list.forEach() in addition to list.stream.forEach() both are valid.
2. Prefer using forEach() amongst streams because streams are lazy in addition to non evaluated until a final functioning is called. 
3. forEach() is a final operation, you lot cannot telephone weep upward whatever method on current after this.
4. When you lot run forEach() method on parallel current the gild on which elements are processed is non guaranteed, though you lot tin utilization forEachOrdered() to impose ordering.
5. forEach() method accepts a Consumer instance, which is a functional interface, that's why you lot tin transcend a lambda appear to it. 

That's all almost how to utilization forEach() method to loop over Stream inwards Java. You tin utilization this technique to acquire over whatever Collection, List, Set or Queue inwards Java. They all allow you lot to acquire a Stream in addition to after telephone weep upward the forEach() method on it. Remember, though, forEach() is a final functioning in addition to you lot cannot telephone weep upward some other method after this. Don't re-use or transcend some streams after calling whatever final functioning on it e.g. forEach().


Further Learning
The Complete Java MasterClass
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How to utilization Stream shape inwards Java 8 (tutorial)

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

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

5 Books to Learn Java 8 from Scratch (books)

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

Java 8 Certification FAQ (guide)

Java 8 Mock Exams in addition to Practice Test (test)

Thanks for reading this article so far. If you lot similar this article in addition to so delight percentage amongst your friends in addition to colleagues. If you lot receive got whatever question, doubt, or feedback in addition to so delight drib a comment in addition to I'll attempt to response your question.

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