Java ArrayList Cheat Sheet: All Methods with Examples

What is Arraylist?
Java ArrayList class uses a dynamic array for storing the elements. It is like an array, but there is no size limit. We can add or remove elements anytime. So, it is much more flexible than the traditional array. It is found in the java.util package. The ArrayList in Java can have the duplicate elements also. It implements the List interface so we can use all the methods of the List interface here. The ArrayList maintains the insertion order internally.

import java.util.ArrayList;
import java.util.Collections;

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

        // 1. CREATE ArrayList

        ArrayList<String> list = new ArrayList<>();
        System.out.println("Created ArrayList: " + list);


        // 2. add() - Add elements

        list.add("Chennai");
        list.add("Mumbai");
        list.add("Delhi");
        list.add("Kolkata");
        System.out.println("\nAfter add()     : " + list);
        // Output: [Chennai, Mumbai, Delhi, Kolkata]


        // 3. add(index, element) - Add at position

        list.add(2, "Bangalore");
        System.out.println("After add(2)    : " + list);
        // Output: [Chennai, Mumbai, Bangalore, Delhi, Kolkata]

        // 4. get() - Get element by index

        String city = list.get(0);
        System.out.println("\nget(0)          : " + city);
        // Output: Chennai

        // 5. set() - Update element

        list.set(1, "Hyderabad");
        System.out.println("After set(1)    : " + list);
        // Output: [Chennai, Hyderabad, Bangalore, Delhi, Kolkata]


        // 6. remove(index) - Remove by index

        list.remove(3);
        System.out.println("After remove(3) : " + list);
        // Output: [Chennai, Hyderabad, Bangalore, Kolkata]

        // 7. remove(object) - Remove by value

        list.remove("Kolkata");
        System.out.println("After remove()  : " + list);
        // Output: [Chennai, Hyderabad, Bangalore]


        // 8. size() - Get size

        System.out.println("\nsize()          : " + list.size());
        // Output: 3


        // 9. contains() - Check element exists

        System.out.println("contains Chennai: " + list.contains("Chennai"));
        // Output: true
        System.out.println("contains Delhi  : " + list.contains("Delhi"));
        // Output: false


        // 10. indexOf() - Get index of element

        System.out.println("\nindexOf Chennai : " + list.indexOf("Chennai"));
        // Output: 0

        // 11. isEmpty() - Check if empty

        System.out.println("isEmpty()       : " + list.isEmpty());
        // Output: false

        // 12. sort() - Sort elements

        Collections.sort(list);
        System.out.println("\nAfter sort()    : " + list);
        // Output: [Bangalore, Chennai, Hyderabad]


        // 13. reverse() - Reverse elements

        Collections.reverse(list);
        System.out.println("After reverse() : " + list);
        // Output: [Hyderabad, Chennai, Bangalore]


        // 14. subList() - Get portion of list

        list.add("Delhi");
        list.add("Mumbai");
        System.out.println("\nFull list       : " + list);
        System.out.println("subList(1,3)    : " + list.subList(1, 3));
        // Output: [Chennai, Bangalore]

        // 15. toArray() - Convert to Array

        Object[] arr = list.toArray();
        System.out.println("\ntoArray()       : ");
        for (Object obj : arr) {
            System.out.println("  " + obj);
        }


        // 16. addAll() - Add multiple elements

        ArrayList<String> newCities = new ArrayList<>();
        newCities.add("Pune");
        newCities.add("Jaipur");
        list.addAll(newCities);
        System.out.println("\nAfter addAll()  : " + list);
        // Output: [Hyderabad, Chennai, Bangalore, Delhi, Mumbai, Pune, Jaipur]

        // 17. clear() - Remove all elements

        list.clear();
        System.out.println("After clear()   : " + list);
        // Output: []
        System.out.println("isEmpty()       : " + list.isEmpty());
        // Output: true
    }
}