How to Implement a Size-Limited Queue in Java

Is there a pre-existing class in Java that implements a fixed-size queue preserving the last N elements while removing the oldest?

import java.util.LinkedList;

public class LimitedQueue<E> extends LinkedList<E> {
    private int limit;

    public LimitedQueue(int limit) {
        this.limit = limit;
    }

    @Override
    public boolean add(E o) {
        super.add(o);
        while (size() > limit) { super.remove(); }
        return true;
    }
}

Java does not provide a built-in size-limited queue. However, you can use a custom implementation or libraries like Apache Commons Collections which can provide similar functionality. Below is a detailed explanation of how to implement a size-limited queue in Java.

import org.apache.commons.collections4.queue.CircularFifoQueue;

// Example of using CircularFifoQueue from Apache Commons Collections
CircularFifoQueue<Integer> queue = new CircularFifoQueue<>(3);
queue.add(1);
queue.add(2);
queue.add(3);
queue.add(4); // This will remove 1 and keep 2, 3, 4
System.out.println(queue); // Output: [2, 3, 4]

Causes

• The Java Collections Framework does not include a specific implementation of a bounded queue that automatically manages size.
• Most queue implementations (like ArrayDeque or LinkedList) allow unbounded sizes.

Solutions

• Implement a custom class extending LinkedList, as shown in the provided code snippet.
• Utilize third-party libraries like Apache Commons Collections, which provides a CircularFifoQueue that can store a limited number of elements.

Mistake: Forgetting to handle synchronization issues in multi-threaded environments.

Solution: Use synchronized methods or consider using ConcurrentLinkedQueue with size management.

Mistake: Trying to use arrays for fixed-size queues without proper management.

Solution: Always prefer dynamic data structures like LinkedList or use the specialized classes from libraries.