Comparing two ArrayLists could be a tricky task for beginner programmers. On this page, we are going to share some of the best ways to compare two ArrayLists.
Compare ArrayLists using Equal[]:
You can easily compare the two ArrayLists by simply using the equals[] method. This method returns a boolean value[True or False]. So, if the result is true, the ArrayLists are equal; otherwise, they are not equal.
Source Code:
import java.util.ArrayList; public class ComparingArrayLists { //using equals[] public static void main[String[] args] { //initializing two array lists ArrayList < String > list1 = new ArrayList < > []; ArrayList < String > list2 = new ArrayList < > []; //storing data in list 1 list1.add["Java"]; list1.add["Python"]; list1.add["C++"]; //storing data in list 2 list2.add["Java"]; list2.add["Python"]; list2.add["C++"]; //printing both lists System.out.println["List 1:" + list1]; System.out.println["List 2:" + list2]; //comparing both lists if [list1.equals[list2]] { System.out.println["Lists are equal"]; } else { System.out.println["Lists are not equal"]; } //adding another element to list 1 list1.add["HTML"]; //comparing both lists again if [list1.equals[list2]] { System.out.println["Lists are equal"]; } else { System.out.println["Lists are not equal"]; } } }Output:
run: List 1:[Java, Python, C++] List 2:[Java, Python, C++] Lists are equal Lists are not equal BUILD SUCCESSFUL [total time: 5 seconds]Compare Arraylists using retainAll[]:
In case you want to compare two ArrayLists with respect to common elements, then you should be trying retainAll[] method. It will return all common elements between two ArrayLists.
Source code:
import java.util.ArrayList; public class ComparingArrayLists {//using retainAll[] public static void main[String[] args] { //initializing two array lists ArrayList list1 = new ArrayList[]; ArrayList list2 = new ArrayList[]; //storing data in list 1 list1.add["Mike"]; list1.add["Sara"]; list1.add["John"]; //storing data in list 2 list2.add["Mike"]; list2.add["Sara"]; list2.add["Diaz"]; list2.add["Sam"]; //printing both lists System.out.println["List 1:" + list1]; System.out.println["List 2:" + list2]; //it will return common elements list2.retainAll[list1]; //printing common elements System.out.println["Common elements are: " + list2]; } }Output:
run: List 1:[Mike, Sara, John] List 2:[Mike, Sara, Diaz, Sam] Common elements are: [Mike, Sara] BUILD SUCCESSFUL [total time: 14 seconds]Compare ArrayLists using contains[]:
An alternate way of retainAll[] is to compare the elements of the ArrayLists using contains[] method. The contains[] method checks whether List 1 has the same element as List 2 at the same index.