Avoiding java.util.ConcurrentModificationException When Sorting Maps in Java

Discover how to efficiently sort student scores stored in a HashMap in Java without experiencing the `ConcurrentModificationException`.
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Understanding the Problem

In the provided code, the goal is to sort student scores stored in a HashMap and output them from greatest to least. However, the method attempted involves iterating over the keys of the HashMap, finding the maximum score, removing that entry, and repeating this process. This approach leads to a ConcurrentModificationException because you're modifying the HashMap (removing entries) while still iterating through it.

Example of the Problematic Code:

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

The above code will produce an error when executing due to the concurrent modification of the HashMap.

The Solution: Avoid Direct Modification

1. Why Modify the Map at All?

Rather than removing elements directly from the HashMap, we can simply sort the entries and print them without changing the structure of the Map. This method not only avoids the ConcurrentModificationException, but it also uses an efficient sorting algorithm that Java provides.

2. Improved Sorting Approach

Here is a refined version of the sorting code that utilizes streams to sort entries by their values without modifying the original HashMap:

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

3. Breakdown of the Solution:

Use of Streams: This approach leverages Java's streams to create a streamlined and readable sorting process.

Efficient Output: Finally, forEach allows us to neatly output the sorted entries without any changes to the original HashMap.

4. Final Implementation

If you utilize the changes above, your code will look structured and concise, as shown below:

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

Conclusion