Java 8 forEach examples

Category : Java | Sub Category : Java 8 Features | By Prasad Bonam Last updated: 2020-09-29 13:25:35 Viewed : 663

Java 8 forEach examples:

Syntax:

* @param action The action to be performed for each element

     * @throws NullPointerException if the specified action is null

     * @since 1.8

     */

    default void forEach(Consumer<? super T> action) {

        Objects.requireNonNull(action);

        for (T t : this) {

            action.accept(t);

        }

    }

1. forEach and Map:

   1.1 Before Java 8 : way to loop a Map.

Example :

  JavaMapTest .java 

import java.util.HashMap;

OutPut:

Animal : Bat Number : 120

Animal : Ant Number : 110

Animal : Cat Number : 130

Animal : Elephant Number : 150

Animal : Dog Number : 140

Animal : Fox Number : 160

1.2 In Java 8 -> loop a Map with forEach with lambda expression

Syntax : 

void java.util.Map.forEach(BiConsumer<? super String, ? super Integer> action) 

The default implementation is equivalent to, for this map: 

 for (Map.Entry<K, V> entry : map.entrySet())

     action.accept(entry.getKey(), entry.getValue());

Example : JavaMapTest .java

 import java.util.HashMap;

OutPut:

forEach1=>

Animal : BatNumber : 120

Animal : AntNumber : 110

Animal : CatNumber : 130

Animal : ElephantNumber : 150

Animal : DogNumber : 140

Animal : FoxNumber : 160

forEach2=>

Animal : Bat Number : 120

Animal : Ant Number : 110

Animal : Cat Number : 130

Animal : Elephant Number : 150

Animal : Dog Number : 140

Different types of dog sounds

Animal : Fox Number : 160

2. forEach and List:

2.1 Before Java 8 : for-loop to loop a List

Example: JavaListTest .java

 import java.util.ArrayList;

OutPut:

Ant

Bat

Cat

Dog

Elephant

2.2 In Java 8 -> List forEach with  lambda expression or method reference.

Syntax:

void java.lang.Iterable.forEach(Consumer<? super T> action)

Example:  JavaListTest .java

import java.util.ArrayList;

import java.util.List;

 

public class JavaListTest {

     public static void main(String[] args) {

           List<String> animals = new ArrayList<>();

           animals.add("Ant");

           animals.add("Bat");

           animals.add("Cat");

           animals.add("Dog");

           animals.add("Elephant");

          

                    // lambda expression

           System.out.println("List forEach 1==>");        

           animals.forEach(animal -> System.out.println(animal));

          

           System.out.println("List forEach 2==>");        

           animals.forEach(animal -> {

                if ("Dog".equals(animal)) {

                      System.out.println(animal);//// Output : Dog

                }

           });

                    //Stream and filter 

           System.out.println("List forEach 3==>");               

           animals.stream()

                        .filter(f -> f.contains("Ant")).forEach(System.out::println);

     }

}

OutPut:

List forEach 1==>

Ant

Bat

Cat

Dog

Elephant

List forEach 2==>

Dog

List forEach 3==>

Ant