Iterate List Using Streams in Java

In Java, a List is an interface that stores a sequence of elements of similar type. Java provides various ways to iterate over a list, such as using a for loop, forEach loop, iterator object, stream, or forEach() method with a lambda expression.

What is Stream in Java?

In Java, a Stream is an interface, which represents a sequence of elements (or objects) supporting sequential and parallel aggregate operations. These operations can be used to produce the desired result.

The Stream interface provides a method named stream(), which is used to create a sequential stream from the current collection (or List). Following is the syntax of the stream() method:

Collection.stream()

Here, the Collection can be List, ArrayList, etc.

Note: The created sequential stream will have the same sequence of element as List.

Example 1

In the following example, we iterate a list {10, 20, 30, 40} using the Stream. We use the stream() method to create a sequential stream from the current list and use forEach() method with lambda expression (->) to iterate over it:

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class iterateList {
   public static void main(String[] args) {
   
      //instantiating a list using ArrayList class
      List<Integer> list = new ArrayList<>();
      
      //adding element to it
      list.add(10);
      list.add(20);
      list.add(30);
      list.add(40);
      
      System.out.println("The list elements are: ");

      //creating a sequential stream using the stream() method
      Stream<Integer> obj = list.stream();

      //iterate over a list using stream
      obj.forEach(e -> {
         System.out.print(e + " ");
      });
   }
}

The above program displays the following output:

The list elements are: 
10 20 30 40 

Example 2

This is another example of iterating a list using a Stream. We create a sequential stream using the stream() method and use forEach() method with lambda expression (->) to iterate over the sequential Stream:

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class iterateList {
   public static void main(String[] args) {
   
      //instantiating a list using ArrayList class
      List<String> languages = new ArrayList<>();
      
      //adding element to it
      languages.add("Java");
      languages.add("JavaScript");
      languages.add("TypeScript");
      languages.add("C++");
      
      System.out.println("The list elements are: ");
      
	  //creating a sequential stream using stream() method
      Stream<String> obj = languages.stream();
	  
	  //iterate over a list using stream
      obj.forEach(lang -> {
         System.out.println(lang + " ");
      });
   }
}

Following is the output of the above program:

The list elements are: 
Java 
JavaScript
TypeScript
C++