Iterate Over ArrayList Using Lambda Expression in Java

The ArrayList class is a resizable array that can be found in java.util package. The difference between a built-in array and an ArrayList in Java is that the size of an array cannot be modified.

Lambda Expression is a feature that was introduced in Java 8. It is useful when we use collections, such as ArrayList, Set, or Map, and we want to perform operations on the elements of these collections.

In this article, we will learn how to iterate over an ArrayList using a lambda expression in Java.

Iterating Over an ArrayList Using Lambda Expressions

There are two main ways to iterate over an ArrayList using a lambda expression:

• Using forEach() Method with Lambda Expression
• Using Method Reference

Using forEach() Method with Lambda Expression

We use the forEach() method of the Iterable interface to iterate over an ArrayList using a lambda expression. The forEach() method takes a lambda expression as an argument, which is applied to each element of the ArrayList.

Syntax

Following is the syntax to iterate over an ArrayList using a lambda expression:

list.forEach(element -> {
   // perform operation on element
});

Example

In the below example, we will create an ArrayList of integers and then use the forEach() method with a lambda expression to print each element of the ArrayList.

import java.util.ArrayList;
import java.util.List;
public class IterateUsingLambda {
   public static void main(String[] args) {
      List<Integer> list = new ArrayList<>();
    
      list.add(1);
      list.add(2);
      list.add(3);
      list.add(4);
      
      list.forEach(element -> System.out.println("Element: " + element));
   }
}

Output

Following is the output of the above code:

Element: 1
Element: 2
Element: 3
Element: 4

Using Method Reference

In addition to using a lambda expression, we can also use a method reference to iterate over an ArrayList. A method reference is a shorthand notation of a lambda expression to call a method.

Syntax

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

Example

In the example below, we will use a method reference to print each element of the ArrayList.

import java.util.ArrayList;
import java.util.List;
public class IterateUsingMethodReference {
   public static void main(String[] args) {
      List<Integer> list = new ArrayList<>();
      
      list.add(1);
      list.add(2);
      list.add(3);
      list.add(4);
      
      list.forEach(System.out::println);
   }
}

Output

Following is the output of the above code:

1
2
3
4