Java 8 forEach loop explained with code samples

Java 8 introduced a lot of new features like functional interfaces, lambda expressions, etc. These provide a totally new way of programming for developers. One such feature is the forEach support added to the Collection interfaces. In this blog post, I will be covering this feature in detail.

Edit

What is forEach

Java 8 added a new method called forEach to all the Collection interfaces via the Iterable interface. You can use this method to iterate through a Collection internally without the need for an explicit for loop.

Before Java 8

Prior to Java 8, if we wanted to iterate through a Collection like a List, we had to write code similar to the following:

public class ForEachDemo {public static void main(String args[]){List <Integer> list = Arrays.asList(5,3,11,15,9);for(int num:list){System.out.println("Number is "+num);}}}

So you need to write a for loop to iterate through the elements in the List. In the body of the for loop, you can write the code that you want to be executed on each element in the list.

Java 8 Way

Starting with Java 8, you can iterate through a Collection using the forEach method.  So you can write code similar to the following:

public class ForEachDemo {public static void main(String args[]){List<Integer> list = Arrays.asList(5,3,11,15,9);list.forEach(num -> System.out.println("Number is "+num));}}

So here, we are invoking the forEach method on the List interface. We are passing a lambda expression to the forEach method that prints the current element.  So, you can see that there is no explicit for loop used here.

How forEach works

Java 8 has added a new method called forEach on the Iterable Interface.  The Collection interface extends this interface and so this method is automatically available in all the Collection interfaces like Set and List

The forEach method accepts a single argument which is a Consumer instance. Consumer is a functional interface. Refer to this blog post to understand more about functional interfaces. Consumer has a single method called accept which accepts input of any data type.

The forEach method is given a default implementation within the Iterable interface. Refer to this blog post to understand default interface methods introduced by Java 8. This is just to avoid making changes to the code for all the Collection classes to provide an implementation for this method. If the default implementation was not provided, Java would have to provide an implementation for the forEach method in each of the Collection classes like ArrayList, HashSet. etc.

The default implementation of the forEach method iterates through all the elements of the Collection on which it is invoked and invokes the accept method with the specified lambda expression. Here we are using a lambda expression that simply prints the input number. So the forEach method invokes the accept method with this expression and prints each number in the input list.

Just like List,  you can use the forEach method to iterate over a Map or Set as well.

Why forEach is better

Compared to the traditional approach, the Java 8 approach is much better. The traditional approach is verbose and requires explicit code to be written. In contrast, the Java 8 code is concise and easy to read.

Comments

Post a Comment

Popular posts from this blog

How to use logging in SpringBoot with code samples

Image
In this article, we will learn how to use logging in SpringBoot. Introduction There are several Java logging frameworks like logback, log4j, and so on. Spring Boot supports out-of-the-box support for logback. Let us learn how to use logging in SpringBoot with logback. Step 1 – Create a New Maven Project Create a new Maven project. (Refer to  this  blog post). This will create a project in Eclipse as follows:   Step 2 – Add the Spring Boot Dependencies Add the spring-boot-starter-web dependency to the pom.xml . So, the pom.xml should look as follows: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.learnjava</groupId> <artifactId>learnjava-springboot-logging-example</artifactId> <version>0.0.1-SNAPSHOT&
Read more

Python While Loop with code samples

Much like a Java while loop, you can use a Python while loop to repeatedly execute a block of code as long as a condition is true. In this article, we will learn more about the Python while loop. Python While loop Syntax A while loop in Python has the following syntax: while <condition>: loop body The while keyword is followed by a condition. If the condition evaluates to true, the body of the loop is executed. Once the body of the loop is completed, the condition is checked again and this is repeated until the condition evaluates to false at which point the loop is exited. While loop Sample Code The following code demonstrates how you can use the while loop: num=10counter=1total=0while counter<=num: total += counter counter+=1print("sum of first 10 numbers is",total) This code adds the numbers from 1 to 10 and prints the sum. It uses a while loop to iterate from 1 to 10. The while loop checks the condition counter <= num and if so adds the current value of count
Read more

How to convert a List to a Set

In this blog post ,I will be showing you how you can convert a List to a Set. Consider the following code snippet: public class ListToSetDemo {public static void main(String[] args) {List<Integer> list = Arrays.asList(5,3,11,15,9);//Method 1Set<Integer> set = new HashSet<Integer>(list);System.out.println("Set is "+set);//method 2Set<Integer> set2 = new HashSet<Integer>();set2.addAll(list);System.out.println("Set is "+set2);}} This code demonstrates two ways to convert a List to a Set. Method 1 Here, we are creating a new HashSet . We are invoking the constructor that accepts a Collection object. Here, we are passing in the input list to this constructor.   Method 2 Here again, we are creating a new HashSet . However, we are using the default constructor. We are then invoking the addAll method and passing in the input list.   When you run this code, it will print the following output: Set is [3, 5, 9, 11, 15]Set is [3, 5, 9, 11, 15] No
Read more