How Can I Dynamically Add Elements to a Collection During Iteration in Java?

Enhancing Iterative Collections with Dynamic Element Addition

The standard Java Iterator API ensures safe collection modifications during iteration, prohibiting external alterations to the collection. However, certain scenarios may require dynamic element addition to the collection while iterating.

Java Iterator Restrictions

The Java Tutorial explicitly cautions against modifying collections during iteration, stating that "Iterator.remove is the only safe way to modify a collection during iteration." Any other modification may result in unspecified behavior.

Alternative Strategy: Dynamic Enqueuing

To circumvent these restrictions, consider constructing a queue (e.g., java.util.LinkedList) that initially contains the elements to be iterated over. If specific elements satisfy a condition during iteration, enqueue additional elements onto the end of the queue.

Utilize the remove() method to incrementally process elements from the queue, maintaining the iteration until the queue is empty. This approach emulates a standard iterative loop with the ability to dynamically add elements.

Example Workflow:

1. Initialize a queue with the original collection elements.
2. Iterate over the queue using poll() to retrieve elements.
3. For elements meeting the condition, enqueue additional required elements onto the queue.
4. Continue iterating and enqueuing until the queue is empty.

This strategy ensures that added elements are also subjected to iteration, controlling potential infinite loops and maintaining a conceptually clean iterative process.

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