Скачать или смотреть How to Save a String Object into an ArrayList and Remove HashMap Elements in Java

Learn how to simplify your ArrayList of HashMaps by extracting specific values in Java. This guide will show you how to efficiently remove unwanted elements and retain only the necessary data with step-by-step explanations.
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This video is based on the question https://stackoverflow.com/q/63654843/ asked by the user 'Ashley' ( https://stackoverflow.com/u/7017565/ ) and on the answer https://stackoverflow.com/a/63654914/ provided by the user 'Govinda Sakhare' ( https://stackoverflow.com/u/3734640/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

Working with collections in Java can often require some manipulation of data structures, especially when you're networking between ArrayList and HashMap. If you're facing a situation where you need to save a String object into an ArrayList while removing specific HashMap elements, this guide is for you. Here, we will walk through a common problem: extracting status_name values from an ArrayList<HashMap<String, String>> while removing the status_ids.

The Problem

Imagine you have an ArrayList<HashMap<String, String>> that looks like this:

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

You want to filter out the status_id part of each HashMap, keeping only the status_name. The expected outcome is:

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

Now, how do we achieve this? Let's break it down into two different methods depending on whether you're using Java 8 or an earlier version.

Solution in Java 8 and Above

If you're working with Java 8 or later, you can leverage the powerful Stream API to achieve the desired outcome concisely. Follow these steps:

1. Utilizing Streams

You can create a stream from the statusList, flatten it, filter based on your criteria, and collect the results into a new list. Here's how to do that:

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

Explanation:

flatMap: This function allows you to convert the stream of HashMap into a stream of Map.Entry<String, String>.

filter: This step filters out only those entries that have the key status_name.

collect: Finally, you collect the filtered entries into a new list.

Solution for Pre-Java 7

If you are not using Java 8 or higher, you'll need to manually iterate over the HashMap entries. Here’s how you do this for the same result:

1. Iteration Method

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

Explanation:

You create a new ArrayList called statusNames to hold your results.

Use a nested loop to go through each HashMap in the statusList and then through each entry in the HashMap.

If the key is status_name, then add that entry to the statusNames list.

Conclusion

By following the methods outlined above, you should be able to simplify your ArrayList<HashMap<String, String>> structures by isolating only the needed values. Whether you're using modern Java features like Streams or sticking with older conventions, both methods are effective in solving the same problem. Happy coding!