How to Join and Sort Two ArrayLists in Java

A step-by-step guide on how to merge, sort, and eliminate duplicates from two ArrayLists in Java.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Joining 2 Arraylists JAVA

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Join and Sort Two ArrayLists in Java

Working with collections in Java is a common task, especially when handling multiple lists of objects, such as contacts in an address book. If you have two ArrayLists filled with Contact objects and need to merge them into one while sorting and eliminating any duplicates, this guide will guide you in achieving that efficiently.

Understanding the Problem

Imagine you have two ArrayLists, contacts1 and contacts2, each populated with Contact objects read from separate source files. Your goal is to create a new ArrayList, allContacts, containing all unique Contact objects from both lists, sorted in a natural order.

The Challenge

Combine Two Lists: You need to merge both lists into a single one.

Remove Duplicates: Ensure that no duplicate contacts exist in the final list.

Sort the Contacts: The merged list should be sorted to maintain order.

Step-by-Step Solution

Step 1: Simplifying the Reading Process

First, let's encapsulate the contact reading functionality into a helper class. This reduces duplicate code by centralizing the contact reading logic.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Implementing the Reading of Contacts

With the helper class in place, you can simplify the methods to read contacts from the two files:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Joining the Contacts

Now let’s add functionality to join the two lists, sort them, and remove duplicates. This can be done using the TreeSet, which stores sorted elements and automatically handles duplicates.

[[See Video to Reveal this Text or Code Snippet]]

Step 4: A More Modern Approach Using Streams

If you're using Java 8 or newer, you might want to use the Stream API, which allows for a cleaner, more functional approach:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following these steps, you can efficiently merge, sort, and eliminate duplicates from two ArrayLists in Java. Leveraging helper methods not only keeps your code clean but also makes it more maintainable and easier to understand.

Whether you choose the traditional approach with TreeSet or the modern Stream API, both methods allow you to manage your contacts intelligently, ensuring that your address book remains organized and functional.

Now, you're ready to tackle similar challenges in your Java applications!