Java Program to Iterate ArrayList using Lambda Expression

May 26, 2023

What is ArrayList in Java ?

In Java, an ArrayList is a class that provides a resizable array implementation of the List interface. It allows you to store and manipulate a collection of objects in a dynamic manner, with the ability to add, remove, and access elements by their index.
Unlike a regular array, an ArrayList can grow and shrink in size dynamically as elements are added or removed. This makes it a more flexible data structure that can adapt to changing needs.

What is Lambda Expression ?

A lambda expression in Java is a way to write a concise and expressive version of an anonymous function. It allows you to define a method that can be passed around as an argument to other methods, or returned from methods like a regular value.

Lambda expressions were introduced in Java 8 as a way to provide a more functional programming style in Java. They are essentially a shorthand way of writing anonymous classes that implement a single abstract method, which is often referred to as a functional interface.

Syntax :

(parameter1, parameter2, ...) -> { statements }

Important : The parameter list specifies the parameters that the lambda expression takes, and the statements within the curly braces specify the body of the lambda expression. If the body of the lambda expression consists of a single expression, the curly braces can be omitted, and the return value of the expression will be automatically returned by the lambda expression.

Steps to Iterate over an ArrayList :

Create an ArrayList
Add elements to the ArrayList using the add() method
Get the size of the ArrayList using the size() method
Iterate over the elements in the ArrayList using a for loop:
a. Get the current element using the get() method
b. Do something with the current element
End the loop

Here’s a pseudo-code of the algorithm :

1. ArrayList myList = new ArrayList
2. myList.add("element1")
   myList.add("element2")
   myList.add("element3")
3. int size = myList.size()
4. for i = 0 to size - 1
     a. String currentElement = myList.get(i)
     b. // Do something with currentElement
5. end for

Explanation : In the above algorithm, we first create an ArrayList, add some elements to it, and then get the size of the ArrayList. We then use a for loop to iterate over the elements in the ArrayList.
Inside the loop, we get the current element using the get() method and then do something with it. This could be printing the element to the console, manipulating it in some way, or anything else that your program needs to do.
When the loop is complete, we have iterated over all elements in the ArrayList.

Example 1 :

Run

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList< String> list = new ArrayList();
        list.add("stack");
        list.add("array");
        list.add("linkList");
        
        // Iterate over the ArrayList using a Lambda expression
        list.forEach((item) -> {
            System.out.println(item);
        });
    }
}

Output :

stack
array
linkList

Explanation : In this program, we create an ArrayList of strings and add some elements to it. Then, we use the forEach method of the ArrayList to iterate over its elements. The forEach method takes a lambda expression as an argument, which defines what should be done with each element of the ArrayList.

Example 2 :

Run

import java.util.ArrayList;

interface MyFunction< T > {
    void apply(T t);
}

public class Main {
    public static void main(String[] args) {
        ArrayList< String> list = new ArrayList< String>();
        list.add("code");
        list.add("java");
        list.add("python");
        
        // Define a lambda expression using a custom functional interface
        MyFunction printItem = (item) -> {
            System.out.println(item);
        };
        
        // Iterate over the ArrayList using the custom functional interface
        list.forEach(printItem::apply);
    }
}

Output :

code
java
python

Explanation : In this program, we create an ArrayList of strings and add some elements to it. Then, we define a custom functional interface MyFunction that has a single abstract method apply that takes a single argument of type T and returns void.
We define a lambda expression that implements this interface, which simply prints out each element of the ArrayList using System.out.println(). Then, we use the forEach method of the ArrayList to iterate over its elements, passing the lambda expression as an argument using the method reference syntax printItem::apply.

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Java Program to Iterate ArrayList using Lambda Expression

What is ArrayList in Java ?

What is Lambda Expression ?

Syntax :

Steps to Iterate over an ArrayList :

Here’s a pseudo-code of the algorithm :

Example 1 :

Output :

Example 2 :

Output :

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