Circular Queue Simulator

Circular Queue Simulator

An array-based queue that treats its array as a ring. Two numbers describe the whole queue: front, the index of the first item, and size, the number of items. The next free slot is not stored but computed: avail = (front + size) % data.length.

How to use it

• Enqueue, Dequeue and Peek run enqueue(item), dequeue() and first(). At each step the current Java line is highlighted and the index arithmetic is shown.
• Capacity N starts an empty queue of that size. When the queue is full chooses between throwing a "full" exception and doubling the array with resize(2 · N).
• Wraparound Example loads N = 5, front = 2, size = 2 (30, 40): enqueue(50) writes to data[4], and the next two writes wrap around to data[0] and data[1].
• Cancel stops the running operation and restores the queue to its state before it.

Reading the views

• Ring view: each sector is one array slot. The red outline marks front; the orange sector is the slot being read or written.
• Array view: the same slots in index order, with ▲front and ▲avail markers. While the array grows, the new array temp appears below.

Notes

• A full queue and an empty queue both have front == avail; only size tells them apart.
• dequeue() writes null into the freed slot so the garbage collector can reclaim the object. No item is ever shifted.
• Growing copies the items in queue order (temp[k] = data[(front + k) % N]) and sets front = 0. A plain Arrays.copyOf would keep the wrapped order and break the queue.

Complexity