10 Examples of forEach() method inwards Java 8

From Java 8 onward, you lot tin ship away iterate over a List or whatever Collection without using whatever loop inwards Java. The novel Stream shape provides a forEach() method, which tin ship away live used to loop over all or selected elements of list in addition to map. forEach() method provides several wages over traditional for loop e.g. you lot tin ship away execute it inwards parallel yesteryear precisely using a parallel Stream instead of regular stream. Since you lot are operating on stream, it likewise allows you lot to filter in addition to map elements. Once you lot are done amongst filtering in addition to mapping, you lot tin ship away utilisation forEach() to operate over them. You tin ship away fifty-fifty utilisation method reference in addition to lambda expression within forEach() method, resulting inwards to a greater extent than clear in addition to concise code. If you lot non started amongst Java 8 notwithstanding than you lot should arrive 1 of your novel twelvemonth resolution for 2016. Coming years volition come across much to a greater extent than adoption of Java 8. If you lot are looking for a skillful mass to larn Java 8, than you lot tin ship away utilisation Java 8 inwards Action, 1 of the best mass most lambda expression, current in addition to other functional aspect of Java 8. For now, let's come across a pair of examples of forEach() inwards Java 8.

How to utilisation forEach() method inwards Java 8

Now you lot know a picayune fleck most the forEach() method in addition to Java 8, it's fourth dimension to come across roughly code examples in addition to explore to a greater extent than of forEach() method inwards JDK 8.

Iterating over all elements of List using forEach()
You tin ship away loop over all elements using Iterable.forEach() method every bit shown below:

List<String> alphabets = novel ArrayList<>(Arrays.asList("aa", "bbb", "cat", "dog"));
alphabets.forEach(s -> System.out.println(s));

This code volition impress every chemical cistron of the listing called alphabets. You tin ship away fifty-fifty supervene upon lambda human face amongst method reference because nosotros are passing the lambda parameter every bit it is to the
System.out.println() method every bit shown below:

alphabets.forEach(System.out::println);

Now, let's come across if you lot desire to add together comma betwixt ii elements than you lot tin ship away produce thence yesteryear using lambda parameters every bit shown inwards the next example

alphabets.forEach(s -> System.out.print(s + ","));

Btw, immediately you lot cannot utilisation method reference immediately because nosotros are doing something amongst lambda parameters. Let's come across roughly other event of forEach() method for doing filtering of elements.

filter in addition to forEach() Example
One of the principal features of Stream API is its capability to filter elements based upon roughly whatever condition. We bring already seen glimpse of powerful characteristic of Stream API inwards my before post, how to utilisation Stream API inwards Java 8, hither nosotros volition come across it over again but inwards the context of forEach() method.

let's immediately exclusively impress elements which start amongst "a", next code volition produce that for you, startWith() is a method of String class, which render true if String is starting amongst String "a" or it volition render false. Once listing is filtered than forEach() method volition impress all elements starting amongst String "a", every bit shown below:

alphabets.stream()
.filter(s -> s.startsWith("a"))
.forEach(System.out::println);

This is cool, right? You tin ship away read the code similar cake, it's much easier than using Iterator or whatever other ways to loop over List inwards Java.

Now, let's filter out exclusively which has length greater than 2, for this purpose nosotros tin ship away utilisation the length() component of String class:

alphabets.stream()
.filter(s -> s.length() > 2)
.forEach(System.out::println);

forEach() in addition to map() Example
So far you lot bring both basic in addition to advanced event of using the forEach() method, origin amongst but iterating over each chemical cistron in addition to and thence along amongst using the filter() method, Let's come across 1 to a greater extent than event of forEach() method along amongst the map() function, which is roughly other fundamental functionality of Stream API.

The map() method of Java 8 allows you lot to transform 1 type to roughly other e.g. inwards our origin event nosotros are using map() to transform a listing of String to a listing of Integer where each chemical cistron represents the length of String. Now, let's impress length of each string using map() function:

alphabets.stream()
.mapToInt(s -> s.length())
.forEach(System.out::println);

That was fun, isn't it? how most the calculating amount of the length of all string? you lot tin ship away produce thence yesteryear using fold operations similar sum() every bit shown inwards the next example:

alphabets.stream()
.mapToInt(s -> s.length())
.sum();

These were roughly of the mutual but rattling useful examples of Java 8's forEach() method, a novel way to loop over List inwards Java. If you lot feeling nostalgist than don't forget to the journey of for loop inwards Java, a recap of for loop from JDK 1 to JDK 8.

Program to utilisation forEach() component inwards Java 8

import java.util.ArrayList; import java.util.Arrays; import java.util.List;  /**  * Java Program to demo How to utilisation forEach() tilt inwards Java8.  * You tin ship away loop over a list, laid or whatever collection using this  * method. You tin ship away fifty-fifty produce filtering in addition to transformation in addition to   * tin ship away run the loop inwards parallel.  *  * @author WINDOWS 8  */ public class Java8Demo {      public static void main(String args[]) {         List<String> alphabets = new ArrayList<>(Arrays.asList("aa", "bbb", "cac", "dog"));                // looping over all elements using Iterable.forEach() method        alphabets.forEach(s -> System.out.println(s));                // You tin ship away fifty-fifty supervene upon lambda human face amongst method reference        // because nosotros are passing the lambda parameter every bit it is to the        // method        alphabets.forEach(System.out::println);                // you lot tin ship away fifty-fifty produce something amongst lambda parameter e.g. adding a comma        alphabets.forEach(s -> System.out.print(s + ","));                        // There is 1 to a greater extent than forEach() method on Stream class, which operates        // on current in addition to allows you lot to utilisation diverse current methods e.g. filter()        // map() etc                alphabets.stream().forEach(System.out::println);                // let's immediately exclusively impress elmements which startswith "a"        alphabets.stream()                .filter(s -> s.startsWith("a"))                .forEach(System.out::println);                // let's filter out exclusively which has length greater than 2        alphabets.stream()                .filter(s -> s.length() > 2)                .forEach(System.out::println);                 // now, let's impress length of each string using map()        alphabets.stream()                .mapToInt(s -> s.length())                .forEach(System.out::println);                // how most calculating amount of length of all string        alphabets.stream()                .mapToInt(s -> s.length())                .sum();      }  }

Important things to remember:

1) forEach() is a terminal operation, which agency in 1 lawsuit calling forEach() method on stream, you lot cannot telephone band roughly other method. It volition effect inwards a runtime exception.

2) When you lot telephone band forEach() on parallel stream, the order of iteration is non guaranteed, but you lot tin ship away ensure that ordering yesteryear calling forEachOrdered() method.

3) There are ii forEach() method inwards Java 8, 1 defined within Iterable in addition to other within java.util.stream.Stream class. If purpose of forEach() is precisely iteration in addition to thence you lot tin ship away straight telephone band it e.g. list.forEach() or set.forEach() but if you lot desire to perform roughly operations e.g. filter or map in addition to thence meliorate origin acquire the current in addition to and thence perform that functioning in addition to lastly telephone band forEach() method.

4) Use of forEach() results inwards readable in addition to cleaner code.

Here are roughly advantages in addition to benefits of Java 8 forEach() method over traditional for loop:

you lot tin ship away iterate over a List or whatever Collection without using whatever loop inwards Java 10 Examples of forEach() method inwards Java 8

That's all most how to utilisation forEach() inwards Java 8. By next these examples, you lot tin ship away easily acquire to speed amongst abide by to using the forEach() method. It's perfect to live used along amongst current in addition to lambda expression, in addition to allow you lot to write loop-free code inwards Java. Now, 1 delineate of piece of occupation for you, how produce you lot break? Does forEach() method allow you lot to interruption inwards between? If you lot know the answer posts every bit a comment.

Further Reading

Top 10 Java 8 Tutorials for Programmers (read here)
5 skillful books to larn Java 8 from scractch (see here)
20 Examples of novel Date adn Time API of JDK 8 (examples)
How to read a file inwards precisely 1 delineate inwards Java 8? (solution)
10 JDK vii features to revise before starting amongst Java 8? (features)
Java SE 8 for Really Impatient yesteryear Cay S. Horstmann (see here)

P.S. : If you lot desire to larn to a greater extent than most novel features inwards Java 8 in addition to thence delight come across the tutorial What's New inwards Java 8. It explains most all of import features of Java 8 e.g. lambda expressions, streams, functional intefaces, Optionals, novel appointment in addition to fourth dimension API in addition to other miscellaneous changes.