Java Viii Foreach() Loop Example

Java 8 has introduced a novel way to loop over a List or Collection, yesteryear using the forEach() method of the novel Stream class. You tin iterate over whatsoever Collection e.g. List, Set or Map yesteryear converting them into a java.util.sttream.Stream instance as well as and so calling forEach() method. This method performs given performance on every chemical component division of Stream, which tin live either merely printing it or doing something else. Since current tin live sequential or parallel, the demeanor of if this method is non deterministic if used alongside a parallel stream. One to a greater extent than affair to retrieve almost the forEach() method is that it's a terminal operation, which agency y'all cannot reuse the Stream after calling this method. It volition throw IllegalStateException if y'all essay to telephone band some other method on this Stream.

Btw, y'all tin too telephone band 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 y'all to a greater extent than choices e.g. filtering, mapping or flattening etc.

In this article, y'all 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 y'all are Java developer alongside some years of experience, pass some fourth dimension learning novel features of Java 8, it's going to live 1 of the most sought after unloose inwards coming years.

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

In this section, I volition become over a pair of mutual scenarios every Java developer confront inwards their solar daytime job. In the offset example, nosotros receive got a listing of prime numbers as well as 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 component division of the current which is an Integer variable as well as passing it to System.out.println() for printing. Since forEach() method accepts a Consumer type, which is a functional interface as well as that's why nosotros tin transcend a lambda expression to it.

You tin fifty-fifty shorten it yesteryear using method reference, every bit shown below:

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

You tin usage method reference inwards house of the lambda human face if y'all are non doing anything alongside the parameter, except passing it to some other method. For example, inwards our side yesteryear side 2 examples, nosotros cannot supersede lambda human face alongside method reference because nosotros are modifying the element.

You tin too run into Java SE 8 for Really Impatient to larn to a greater extent than almost method reference as well as lambda expression, 1 of the amend 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 exclusively impress fifty-fifty numbers from the listing of primes:

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

filter() method from Stream cast await a Predicate instance which is too a functional interface, alongside exactly 1 method which returns boolean type, therefore y'all tin usage a lambda human face which returns boolean inwards house of Predicate.

Java 8 forEach example

You tin write to a greater extent than code yesteryear next above techniques, I propose y'all experiment alongside dissimilar current methods to larn more.  Here is my sample plan to demonstrate how to usage forEach() tilt to iterate over every chemical component division of a list, fix or current 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 component division of list         // inwards this instance nosotros are using method reference becasue         // nosotros are non doing anything alongside each chemical component division of collection         // as well as 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 component division 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 + ","));                     // y'all tin too usage forEach alongside parallel stream         // gild volition non live 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 into from the output that forEach() tilt plant exactly similar for loop but it is much to a greater extent than powerful merely because y'all tin perform the looping inwards parallel without writing a unmarried delineate of multi-threading code.

Here is the some other forEach() method defined inwards the Iterable interface, y'all tin usage it straight without calling the stream() method because List, Set or Queue implements Collection as well as Iterable interface.

Advantages of forEach() over for loop inwards Java 8 

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

• More succinct code, sometimes exactly 1 liner
• You tin transcend lambda expression, which gives y'all the immense flexibility to change what y'all create inwards the loop.
• forEach looping tin live made parallel alongside minimal endeavor e.g. without writing a unmarried delineate of concurrent code, all y'all take away to create is telephone band parallelStream() method. 

Important points almost 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() as well as list.stream.forEach() both are valid.
2. Prefer using forEach() alongside streams because streams are lazy as well as non evaluated until a lastly performance is called. 
3. forEach() is a lastly operation, y'all cannot telephone band whatsoever method on current after this.
4. When y'all run forEach() method on parallel current the gild on which elements are processed is non guaranteed, though y'all tin usage forEachOrdered() to impose ordering.
5. forEach() method accepts a Consumer instance, which is a functional interface, that's why y'all tin transcend a lambda human face to it. 

That's all almost how to usage forEach() method to loop over Stream inwards Java. You tin usage this technique to become over whatsoever Collection, List, Set or Queue inwards Java. They all allow y'all to acquire a Stream as well as afterward telephone band the forEach() method on it. Remember, though, forEach() is a lastly performance as well as y'all cannot telephone band some other method after this. Don't re-use or transcend to a greater extent than or less streams after calling whatsoever lastly performance on it e.g. forEach().


Further Learning
The Complete Java MasterClass
tutorial)

How to usage Stream cast inwards Java 8 (tutorial)

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

How to usage 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 usage 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 as well as Practice Test (test)

Thanks for reading this article so far. If y'all similar this article as well as so delight part alongside your friends as well as colleagues. If y'all receive got whatsoever question, doubt, or feedback as well as so delight driblet a comment as well as I'll essay to answer your question.

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