Detailed explanation of commonly used Java Queue queue methods and precautions

Common methods and precautions for Java Queue queue

Queue (Queue) is a special linear data structure. Its operation is based on first-in, first-out (FIFO) ) principle. Java provides the Queue interface to implement queue functions. Common implementation classes include LinkedList and ArrayDeque.

1. Commonly used methods

1. add(): Add an element to the end of the queue. If the queue is full, using this method will throw an IllegalStateException.

   Queue<Integer> queue = new LinkedList<>();
   queue.add(1);
   queue.add(2);
   queue.add(3);

2. offer(): Add an element to the end of the queue. If the queue is full, using this method will return false, indicating that the addition failed.

   Queue<Integer> queue = new LinkedList<>();
   queue.offer(1);
   queue.offer(2);
   queue.offer(3);

3. remove(): Remove and return the head element of the queue. If the queue is empty, using this method will throw a NoSuchElementException exception.

   Queue<Integer> queue = new LinkedList<>();
   queue.add(1);
   queue.add(2);
   queue.add(3);
   int head = queue.remove();

4. poll(): Remove and return the head element of the queue. If the queue is empty, using this method will return null.

   Queue<Integer> queue = new LinkedList<>();
   queue.offer(1);
   queue.offer(2);
   queue.offer(3);
   int head = queue.poll();

5. element(): Returns the head element of the queue, but does not delete it. If the queue is empty, using this method will throw a NoSuchElementException exception.

   Queue<Integer> queue = new LinkedList<>();
   queue.add(1);
   queue.add(2);
   queue.add(3);
   int head = queue.element();

6. peek(): Returns the head element of the queue, but does not delete it. If the queue is empty, using this method will return null.

   Queue<Integer> queue = new LinkedList<>();
   queue.offer(1);
   queue.offer(2);
   queue.offer(3);
   int head = queue.peek();

2. Notes

1. The implementation classes of queues are usually thread-unsafe. If used in a multi-threaded environment, you need to Perform additional synchronization.

   Queue<Integer> queue = new LinkedList<>();
   queue = Collections.synchronizedQueue(queue);

2. Consider the size of the queue. If the capacity is limited, capacity judgment and processing need to be performed before adding elements.

   Queue<Integer> queue = new ArrayDeque<>(10);

3. Avoid using Iterator for traversal and deletion operations. Instead, use the methods provided by the queue.
4. When you need to use a priority queue, you can use the PriorityQueue class to implement it.
5. Queue is very useful in solving first-in-first-out problems, such as task scheduling, breadth-first search and other scenarios.

Summary:
Java's Queue queue provides a series of methods to implement first-in, first-out operations. Common methods include add(), offer(), remove(), poll() , element() and peek(). When using queues, you need to pay attention to thread safety, capacity issues and traversal delete operations. Queues are very convenient and practical when solving first-in-first-out problems, and are suitable for scenarios such as task scheduling and breadth-first search.

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