kunal-kushwaha/DSA-Bootcamp-Java · error · Exception

Queue is empty

Error message

Queue is empty

What it means

CircularQueue.remove() throws a checked java.lang.Exception when the queue is empty, because there is no element to dequeue. The throws clause forces callers to handle the underflow condition at compile time.

Solutions

1. Guard with if (!queue.isEmpty()) before calling remove().
2. Catch Exception around remove() and treat empty as a normal condition.
3. Use queue.size()/isEmpty() in loop conditions instead of a fixed count.

Example fix

// before
int val = queue.remove();
// after
if (!queue.isEmpty()) {
    int val = queue.remove();
}

if (!cq.isEmpty()) {
    int val = cq.remove();
}

try {
    int val = cq.remove();
} catch (Exception e) {
    // queue was empty — treat as normal, e.g. break the consume loop
}

When it happens

Trigger: Calling remove() on a CircularQueue where size == 0 (isEmpty() true): dequeuing more times than insert() was called, or removing before any insert.

Common situations: Consumer loops draining a queue faster than producers fill it; off-by-one loop bounds consuming one extra element; calling remove() on a freshly constructed queue.

Related errors

• Queue is empty
• Removing from an empty heap!
• Removing from empty Heap
• Cannot pop from an empty stack!!
• Cannot peek from an empty stack!!

AI-assisted analysis of kunal-kushwaha/DSA-Bootcamp-Java@6bc4d8bf8a (2026-08-31). Data as JSON: /api/errors/b6a62d5acaeebe28. Report an issue: GitHub.

Appendix: source

Thrown at lectures/19-stacks-n-queues/code/src/com/kunal/CircularQueue.java:39

    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean insert(int item) {
        if (isFull()) {
            return false;
        }
        data[end++] = item;
        end = end % data.length;
        size++;
        return true;
    }

    public int remove() throws Exception {
        if (isEmpty()) {
            throw new Exception("Queue is empty");
        }

        int removed = data[front++];
        front = front % data.length;
        size--;
        return removed;
    }

    public int front() throws Exception{
        if (isEmpty()) {
            throw new Exception("Queue is empty");
        }
        return data[front];
    }

    public void display() {
        if (isEmpty()) {
            System.out.println("Empty");

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