How to Efficiently Iterate Over a List of Java Objects Using Java 8

Learn how to navigate through a list of lists of Java objects and count distinct IDs using Java 8 Stream features.
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How to Efficiently Iterate Over a List of Java Objects Using Java 8

In today's digital landscape, handling collections of objects in Java is a fundamental skill for developers. With the introduction of Java 8, we gained powerful Stream APIs that simplified how we iterate and manipulate data collections. This guide will guide you through iterating over a list of lists of objects and counting distinct IDs, specifically focusing on customer data.

Problem Definition

You might encounter scenarios where you're working with a list of lists of Java objects. For instance, suppose you need to loop through multiple customer issues, each containing a list of customer edits, and you need to identify distinct customer IDs efficiently.

Here's the question we are answering: How to iterate through a list of lists of Java objects using Java 8?

The Solution in Steps

To tackle this task, we will break the solution down into clear sections. First, let’s look at how we set up our data model, followed by the method to process the data.

Step 1: Creating the Data Model

For this example, we will define two Plain Old Java Objects (POJOs): CustomerIssues and CustomerEditVO.

CustomerIssues

A container for a list of CustomerEditVO items and a comment.

CustomerEditVO

Represents individual customer edits with a unique customer ID and units.

Here's the implementation:

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

Step 2: Populate the Data

Next, we will initialize our data for some customer issues:

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

Step 3: Iterating and Collecting Data

With our data model in place, we can use Java 8 Stream features to process the data:

Flatten the Structure: Transform the list of lists into a single list.

Extract Distinct Customer IDs: Collect distinct customer IDs from the flattened list.

Here’s the code that achieves this:

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

Key Points to Remember

POJO Structures: Ensure you override equals() and hashCode() methods in your POJO to allow proper distinct counting based on the customer ID.

Stream Operations: Utilize flatMap() to convert a list of lists into a single-level list.

Distinct Collection: Use the distinct() method in Streams to filter unique elements.

Conclusion

Iterating through a list of lists with Java 8 Streams can be both efficient and elegant. By following the steps outlined in this guide, you can easily process collections, flatten them, and extract unique identifiers like customer IDs. The flexibility of the Stream API allows for clean and maintainable code.

I hope this comprehensive guide simplifies your approach to handling collections in Java. Happy coding!