Comparing two ArrayList In Java

Last Updated : 07 Oct, 2022

Java provides a method for comparing two Array List. The ArrayList.equals() is the method used for comparing two Array List. It compares the Array lists as, both Array lists should have the same size, and all corresponding pairs of elements in the two Array lists are equal.

Example:

Input : ArrayList1 = [1, 2, 3, 4],
        ArrayList2 = [1, 2, 3, 4]
Output: Array List are equal

Input : ArrayList1 = [1, 2, 3, 4],
        ArrayList2 = [4, 2, 3, 1]
Output: Array List are not equal

Syntax:

boolean equals(Object o)

Parameters: This function has a single parameter which is an object to be compared for equality.

Returns: This method returns True if Array lists are equal.

Implementation:

Java

// Comparing two ArrayList In Java
import java.util.ArrayList;

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

        // create two Array List
        ArrayList<String> ArrayList1
            = new ArrayList<String>();
        ArrayList<String> ArrayList2
            = new ArrayList<String>();

        // insert items in ArrayList 1
        ArrayList1.add("item 1");
        ArrayList1.add("item 2");
        ArrayList1.add("item 3");
        ArrayList1.add("item 4");

        // insert items in ArrayList 2
        ArrayList2.add("item 1");
        ArrayList2.add("item 2");
        ArrayList2.add("item 3");
        ArrayList2.add("item 4");

        // Display both ArrayList
        System.out.println(" ArrayList1 = " + ArrayList2);
        System.out.println(" ArrayList1 = " + ArrayList1);

        // compare ArrayList1 with ArrayList2
        if (ArrayList1.equals(ArrayList2) == true) {
            System.out.println(" Array List are equal");
        }
        else
        // else block execute when
        // ArrayList are not equal
        {
            System.out.println(" Array List are not equal");
        }

        // insert one more item in ArrayList 1
        System.out.println(
            "\n Lets insert one more item in Array List 1");
        ArrayList1.add("item 5");

        // display both ArrayList
        System.out.println(" ArrayList1 = " + ArrayList1);
        System.out.println(" ArrayList = " + ArrayList2);

        // again compare ArrayList 1 with ArrayList 2
        if (ArrayList1.equals(ArrayList2) == true) {
            System.out.println(" Array List are equal");
        }
        else {
            System.out.println(" Array List are not equal");
        }
    }
}

Output

 ArrayList1 = [item 1, item 2, item 3, item 4]
 ArrayList1 = [item 1, item 2, item 3, item 4]
 Array List are equal

 Lets insert one more item in Array List 1
 ArrayList1 = [item 1, item 2, item 3, item 4, item 5]
 ArrayList = [item 1, item 2, item 3, item 4]
 Array List are not equal

Time Complexity: O(N), where N is the length of the Array list.