How to Efficiently Join Two Lists of Different Types in Java Using stream()

Learn how to join two lists of different signature types in Java with a common property using the `stream()` method. This guide walks you through an efficient solution.
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Joining Two Lists of Different Signature Types in Java Using stream()

Managing collections in Java can sometimes feel overwhelming, especially when you need to compare and join lists with different types. In this guide, we'll tackle a specific problem: How to efficiently update a list of winner coupons based on a list of scanned coupons. This is a common scenario, especially in applications dealing with promotions or contests where users scan codes to see if they've won something.

The Problem Explained

Suppose you have two Java classes: ScannedCoupon and WinnerCoupon, defined as follows:

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

You also have two lists:

scannedCouponList containing 30 ScannedCoupon items

winnerCouponList containing 200 WinnerCoupon items

The goal is to update the won property in winnerCouponList to true for any WinnerCoupon where its winnercode matches a scannedcode from the scannedCouponList. As the winner list is much larger, you want to avoid looping through the scanned list for every winner coupon, which would be inefficient.

The Efficient Solution

Using Java Streams provides a clean and efficient way to solve this problem without traditional looping. Let’s break down the steps.

Step 1: Collect Scanned Codes into a Set

First, you can retrieve the scannedcode values from the scannedCouponList and store them in a Set. This allows for fast lookups, as the contains method for a Set has an average time complexity of O(1).

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

Step 2: Update winnerCouponList Using Streams

Next, you will need to iterate through the winnerCouponList to check if each winnercode is present in the scannedCodes set. If a match is found, simply set the won property to true.

Here is how you can do this using streams:

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

Explanation of This Process

Filtering: The filter() method checks if the current winnercode exists in the scannedCodes set.

Updating: The forEach() method is used to set the won property to true for all matched items.

Complexity Consideration

This method significantly reduces the overhead by taking advantage of the Set's fast lookup capabilities. The overall time complexity, therefore, is approximately O(n), where n represents the size of the winnerCouponList. This is efficient since the operation is primarily based on the larger list while only using a small collection of codes for the lookup.

Conclusion

By using Java Streams, you can efficiently join and update two lists of different types based on shared properties without the overhead of nested loops. This not only makes your code cleaner but also enhances performance, especially when dealing with larger datasets.

If you have more cases like this or need further explanations on Java Streams, feel free to reach out in the comments below!