How to Use an ArrayList in Java: A Comprehensive Guide with Code Examples

Creating an ArrayList

To create an ArrayList in Java, you need to import the java.util.ArrayList class. Here’s how you can declare and initialize an ArrayList:

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Create an ArrayList of Strings
        ArrayList list = new ArrayList<>();
        list.add("Java");
        list.add("Python");
        list.add("C++");
        
        // Display the ArrayList
        System.out.println(list);
    }
}
        

In this example, we’ve created an ArrayList of Strings and added a few programming languages to it using the add() method. The System.out.println() statement is used to print the ArrayList.

Common ArrayList Methods

ArrayLists provide various methods that make working with them easy. Here are some commonly used methods:

• add(E e): Adds an element to the ArrayList.
• get(int index): Returns the element at the specified index.
• remove(int index): Removes the element at the specified index.
• size(): Returns the number of elements in the ArrayList.
• contains(Object o): Checks if the ArrayList contains the specified element.

Let’s demonstrate some of these methods with an example:

import java.util.ArrayList;

public class ArrayListMethodsExample {
    public static void main(String[] args) {
        ArrayList languages = new ArrayList<>();
        languages.add("Java");
        languages.add("Python");
        languages.add("C++");
        
        // Accessing an element using get()
        System.out.println("Element at index 1: " + languages.get(1));
        
        // Removing an element using remove()
        languages.remove(2);
        
        // Checking if the ArrayList contains an element
        System.out.println("Contains 'Python'? " + languages.contains("Python"));
        
        // Printing the ArrayList after removal
        System.out.println("Updated ArrayList: " + languages);
    }
}
        

Iterating Over an ArrayList

One of the common tasks when working with an ArrayList is iterating over its elements. You can use several methods to do this:

• Using a for loop
• Using a for-each loop
• Using the Iterator interface

Here’s an example that demonstrates all of these methods:

import java.util.ArrayList;
import java.util.Iterator;

public class ArrayListIterationExample {
    public static void main(String[] args) {
        ArrayList languages = new ArrayList<>();
        languages.add("Java");
        languages.add("Python");
        languages.add("C++");

        // Using a for loop
        System.out.println("Using for loop:");
        for (int i = 0; i < languages.size(); i++) {
            System.out.println(languages.get(i));
        }

        // Using for-each loop
        System.out.println("Using for-each loop:");
        for (String language : languages) {
            System.out.println(language);
        }

        // Using Iterator
        System.out.println("Using Iterator:");
        Iterator iterator = languages.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}