Java Queue Interface: Methods and Examples for AP Computer Science A

📚 Quick Study Guide

• 🔑 Queue Interface: Represents a FIFO (First-In, First-Out) data structure.
• ➕ enqueue(element): Adds an element to the rear of the queue (known as `add()` or `offer()` in Java).
• ➖ dequeue(): Removes and returns the element at the front of the queue (known as `remove()` or `poll()` in Java).
• 👀 peek(): Returns the element at the front of the queue without removing it.
• 📏 size(): Returns the number of elements in the queue.
• ✅ isEmpty(): Returns `true` if the queue is empty, `false` otherwise.
• ❗ Common Implementations: `LinkedList` and `ArrayDeque` are commonly used to implement the Queue interface in Java.

Practice Quiz

1. Which of the following best describes the behavior of a Queue?
   1. A. Last-In, First-Out (LIFO)
   2. B. First-In, First-Out (FIFO)
   3. C. Random Access
   4. D. No specific order
2. Which method is used to add an element to the rear of a Queue in Java?
   1. A. `pop()`
   2. B. `push()`
   3. C. `add()`
   4. D. `remove()`
3. Which method is used to remove and return the element at the front of a Queue in Java?
   1. A. `peek()`
   2. B. `add()`
   3. C. `poll()`
   4. D. `offer()`
4. What does the `peek()` method do in a Queue?
   1. A. Removes the last element.
   2. B. Returns the element at the front without removing it.
   3. C. Adds an element to the rear.
   4. D. Removes the first element.
5. Which of the following is a common implementation of the Queue interface in Java?
   1. A. `ArrayList`
   2. B. `HashSet`
   3. C. `LinkedList`
   4. D. `TreeMap`
6. What is the return type of the `isEmpty()` method in the Queue interface?
   1. A. `int`
   2. B. `String`
   3. C. `boolean`
   4. D. `void`
7. If a queue contains the elements [10, 20, 30] (where 10 is the front), what will `poll()` return?
   1. A. `10`
   2. B. `20`
   3. C. `30`
   4. D. `null`