Java 8 – ForEach Example | Iterate Collection in Java

All the Collection Interfaces in Java (List, Set, Map etc) will be extending the Iterable interface as the super interface. In Java 8 a new method has been introduced for Iterating over collections in Java.

void forEach(Consumer<? super T> action)

In this Java 8, ForEach Example article lets see how to iterate through a List and Map with the new forEach Loop in Java 8.

Iterate through ArrayList in Java using forEach Loop

Using Java 7 or less

package com.javainterviewpoint;

import java.util.ArrayList;

public class Iterate_ArrayList
{
    public static void main(String[] args)
    {
        //Create a new ArrayList
        ArrayList countryList = new ArrayList();
        
        //Add elements to the countryList
        countryList.add("India");
        countryList.add("England");
        countryList.add("Australia");
        countryList.add("Japan");
        
        //iterate through list in java
        for (String country : countryList)
        {
            System.out.println(country);
        }
    }
}

Using Java 8 ForEach Example ArrayList

package com.javainterviewpoint;

import java.util.ArrayList;

public class Iterate_ArrayList
{
    public static void main(String[] args)
    {
        //Create a new ArrayList
        ArrayList countryList = new ArrayList();
        
        //Add elements to the countryList
        countryList.add("India");
        countryList.add("England");
        countryList.add("Australia");
        countryList.add("Japan");
        
        //iterate through list in Java 8 using forEach Lambda Expression
        countryList.forEach(country->System.out.println(country));
        
        //iterate through list in Java 8 using forEach method reference
        countryList.forEach(System.out::println);
    }
}

Output: 

 

 

 

 

Iterating a Map in Java using forEach Loop

Using Java 7 or less

package com.javainterviewpoint;

import java.util.HashMap;
import java.util.Map;

public class Iterate_Map
{
    public static void main(String[] args)
    {
        // Create a new HashMap
        HashMap<String, String> countryMap = new HashMap<String, String>();

        // Add elements to the countryMap
        countryMap.put("1", "India");
        countryMap.put("2", "England");
        countryMap.put("3", "Australia");
        countryMap.put("4", "Japan");
        
        //iterate through map in java
        for (Map.Entry<String, String> entry : countryMap.entrySet())
        {
            System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
        }
    }
}

Using Java 8 forEach Map

package com.javainterviewpoint;

import java.util.HashMap;
import java.util.Map;

public class Iterate_Map
{
    public static void main(String[] args)
    {
        // Create a new HashMap
        HashMap<String, String> countryMap = new HashMap<String, String>();

        // Add elements to the countryMap
        countryMap.put("1", "India");
        countryMap.put("2", "England");
        countryMap.put("3", "Australia");
        countryMap.put("4", "Japan");
        
        //iterate through map in Java 8 using forEach Lambda Expression
        countryMap.forEach((key,value)->System.out.println("Key : "+ key+" Value: "+value));
    }
}

Output :

Key : 1 Value: India
Key : 2 Value: England
Key : 3 Value: Australia
Key : 4 Value: Japan