How to groupBy and Count Items in a Map Object in Java

Learn how to efficiently group and count items in a Map object using Java's powerful Stream API. This guide provides a step-by-step breakdown.
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Grouping and Counting Items in Java: A Guide to Using the Map Object

When working with lists in Java, you may find yourself needing to group items and count their occurrences based on specific fields. This guide will explore how to achieve this using a list of Booking objects, specifically grouping them by an OfficeType enum and counting the instances for each type efficiently using Java's Stream API.

Understanding the Problem

Let's say you have a list of Booking objects retrieved from a database, and each Booking includes an officeType field defined as an enum. Your goal is to create a Map where the key is the OfficeType, and the value is the count of bookings for each type.

Example Structure of Booking

Here is a simplified version of the Booking class you'll be working with:

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

Sample Data Retrieval

You would typically retrieve the list of Booking objects as follows:

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

Now, let’s delve into the solution for grouping and counting these bookings by officeType.

The Solution: Using Streams to Group and Count

Step-by-Step Breakdown

Create a Stream from the List: Start by turning your bookingList into a stream to enable functional operations.

Code Implementation

Here’s how you can implement the solution in code:

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

Explanation of the Code

Resulting Map Structure

The final Map<OfficeType, Long> will hold the counts of each OfficeType, making it easy to return to the client or utilize in further processing.

Conclusion

Feel free to ask any questions or share your experiences with grouping data in Java!