ArrayList class in Java

ArrayList is a resizable-array implementation of the List interface. ArrayList offers an alternative to traditional arrays which are fixed in size and cannot grow beyond the capacity specified during initialization.

The ArrayList class also offers a lot of useful methods which we can use in our programs. It implements all optional list operations, and permits all elements, including null.

Java provides the ArrayList class as part of the Java Collections Framework. For an overview of the Java Collections Framework, check out my post Overview of the Java Collections Framework.

The following example illustrates the ArrayList class.

Example

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {

        // create an array list of strings
        ArrayList<String> arrayList = new ArrayList<String>();

        // add some strings into the array list
        arrayList.add("red");
        arrayList.add("blue");
        arrayList.add("green");
        arrayList.add("yellow");

        // display the array list
        System.out.println("Current elements in the array list: " + arrayList);

        // add strings at the specified index
        arrayList.add(0, "black");
        arrayList.add(2, "white");

        // display the array list
        System.out.println("Current elements in the array list: " + arrayList);

        // display the string at a specified index
        System.out.println("Element at index " + 3 + " is " + arrayList.get(3));

        // replace the string at a specified index
        arrayList.set(3, "orange");

        // remove the string at a specified index
        arrayList.remove(1);

        // check if the array list contains a specified string
        System.out.println("Array list contains green: " + arrayList.contains("green"));

        // get the size of the array list
        System.out.println("Number of elements in the array list is " + arrayList.size());
        
    }
}

Output

Current elements in the array list: [red, blue, green, yellow]
Current elements in the array list: [black, red, white, blue, green, yellow]
Element at index 3 is blue
Array list contains green: true
Number of elements in the array list is 5

The above program showed the use of some of the common methods of the ArrayList class. For a complete list of all the available methods, refer the official docs.

Now since you know how to use the ArrayList class, check out another implementation of the List interface, the LinkedList class in Java.