How to Implement a Fixed-Size Queue in Java?

Implementing a Size-Limited Queue in Java

Developers often encounter the need for a data structure that maintains a fixed size while continuously adding elements. In Java, implementing a size-limited queue is straightforward but requires manual coding. However, alternatives exist within external libraries.

Apache Commons Collections 4 introduces the CircularFifoQueue class, which aligns with the desired functionality:

"CircularFifoQueue is a first-in first-out queue with a fixed size that replaces its oldest element if full."

Example Usage with Generics:

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

// Create a queue with a limit of 2 elements
CircularFifoQueue<Integer> fifo = new CircularFifoQueue<>(2);

// Add elements
fifo.add(1);
fifo.add(2);

// Add a third element (replaces oldest element, in this case 1)
fifo.add(3);

// Print the queue
System.out.println(fifo); // Output: [2, 3]

Example Usage with Non-Generics (Apache Commons Collections 3):

import org.apache.commons.collections.buffer.CircularFifoBuffer;

// Create a queue with a limit of 2 elements
CircularFifoBuffer fifo = new CircularFifoBuffer(2);

// Add elements
fifo.add(1);
fifo.add(2);

// Add a third element (replaces oldest element, in this case 1)
fifo.add(3);

// Print the queue
System.out.println(fifo); // Output: [2, 3]

Utilizing these ready-made classes simplifies the implementation of size-limited queues in Java while ensuring efficiency and preventing code duplication.

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