Finding Matching Objects in Two Array Lists Using Java Streams

Learn how to efficiently find matching objects from two Array Lists in Java, even when lists contain duplicates, using Java Streams and custom comparison methods.
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Finding Matching Objects in Two Array Lists Using Java Streams

In programming, it's common to deal with duplicate entries and the need to filter values based on specific criteria. A common question that arises, particularly in Java development, is how to efficiently find objects that match identically across two lists. In this guide, we’ll dive into how to achieve this using Java's powerful Stream API.

Problem Overview

Assume you have two lists containing objects of a custom type called Position. Each Position object has the following attributes:

String account

String date

String cycle

String status

Sample Lists

Let's consider the following sample data for ListA and ListB:

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Based on this data, we want to find accounts that are represented in both lists with identical objects. For instance, ACC1 appears in both lists with matching attributes, while ACC2 is excluded due to differing status values, and ACC3 is excluded as it does not appear in ListB.

Solution Approach

Step 1: Define the Position Class

Firstly, to make our position comparison effective, we must ensure that we properly define the Position class with equals and hashCode methods overridden. Below is how you would define the class:

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Step 2: Using Java Streams to Find Matches

Using Java Streams, we can process ListA and ListB, grouping the positions by account and then comparing the lists. Here’s how you can do this:

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Step 3: Manual Comparison If Necessary

If overriding equals and hashCode is undesired (due to external constraints), you can perform a field-by-field comparison using a BiPredicate. Here's how you can implement it:

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

Conclusion

Finding matching objects across two Array Lists in Java can be efficiently achieved through the use of Java Streams, allowing for clean and understandable code. By defining a proper object equality mechanism or employing manual field comparison when needed, we can filter out duplicates and retain only the desired entries. Implementing these strategies will help ensure that you can handle such data comparison tasks effectively in your Java applications.

For further reading, don't hesitate to explore more about Java Streams and how they can enrich your data manipulation tasks!