Скачать или смотреть How to return a parameter based on another parameter in a List of Objects in Java

Discover how to use Java Streams to fetch specific attributes from a list of objects based on a parameter. Get simple methods to extract values effortlessly!
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How to return a parameter based on another parameter in a List of Objects in Java

Working with lists of objects can sometimes present a challenge, especially when you are trying to fetch specific parameters based on certain conditions. For instance, you might want to extract the amount of an InventoryItem where the name matches a given value. Luckily, this is not only possible but can be done in a very concise manner using Java Streams. In this guide, we'll explore how to achieve this step by step.

The Problem Description

Let’s start by defining the scenario:

You have a class called InventoryItem, which represents individual items in an inventory. Each item has properties like name and amount. When you’re provided with an Inventory object containing a list of such items, you may want to find out the amount of an item based on its name.

Here's an example of how your InventoryItem class may look:

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

Now, if you have an Inventory with a list of these InventoryItem objects, you might be tempted to use Streams for retrieving the amount. Your initial attempt may look like this:

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

However, this code returns the entire InventoryItem, but you only need the amount. So, how do you tweak this approach to extract just the value you want?

The Solution: Using Java Streams Effectively

To achieve your goal, you will need to use terminal operations with your stream in order to process and return the value you need. Below is a detailed breakdown of two easy methods you can employ:

Method 1: Using findFirst()

The findFirst() method will allow you to retrieve the first matching item from the stream, from which you can then get the amount. Here’s how you can implement this:

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

Method 2: Collecting to List

If you want to keep all matches instead of just fetching the first one, use the collect() method to create a list of matched items:

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

Conclusion

Using Java Streams for filtering and retrieving properties of objects in a list is both powerful and straightforward. By employing terminal operations like findFirst() and collect(), you can easily obtain the desired amount based on the name of the item.

With these methods at your disposal, you can now proceed confidently with managing your inventory and extracting the necessary information as needed. Happy coding!