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
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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);
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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);
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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();
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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();
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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();
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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
-
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);
-
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);
- Avoid using Iterator for traversal and deletion operations. Instead, use the methods provided by the queue.
- When you need to use a priority queue, you can use the PriorityQueue class to implement it.
- 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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