![]() This is similar to the previous example’s LinkedList operation, but note the head element is 1 because it’s a PriorityQueue. Example #5 – Examine operation on PriorityQueue We printed the queue after performing the peek operation, and you can observe that the head element, which is 5, remains unchanged in the queue. Note here that we have used the peek() function, which will return the head of the queue without actually removing it. Example #4 – Examine operation on LinkedList The removal is based totally on the value of elements. Note the insertion order and removal orders are not the same. Here, we have used PriorityQueue, which will hold and return the elements depending upon the elements’ natural ordering or upon the comparator, if any passed. Example #3 – Insertion and Removal Operation on PriorityQueue After removing all the elements, we printed the queue and obtained an empty bracket at the end. The removal order is the same as per the insertion. Here, we have used the function isEmpty() to check when the queue becomes empty after removing elements. ![]() Example #2 – Let’s remove the added elements one by one ![]() Note here that the order of insertion is the same with output from left to write. Given below are the different examples of Queue in Java: Example #1 – Add operation with LinkedList implementation Still, in the case of examination, the object will be returned without actually removing from the queue. In the case of the remove operation, an object will be removed from the queue. There are three types of operation in this kind of operation: insertion, the second is removal, and the third is retrieval or examination. So as explained, two types of methods throw an exception and return a special value. A head in a queue concept always represents the first element in the queue upon removal, this head element will be removed first.īelow are all the methods available in the queue:.All the methods available in a queue can be divided into two categories the first type of method throws an exception in case of failure of the operation, such as no element found, and in the second type of method, instead of the exception, any specific value such as null or false is returned in case of operation failure.These are the two basic operations that are supported by a queue.As the queue supports the FIFO structure, it allows the insertion of the elements from one end and removes the elements from another (front) end.The queue provides only a way to define the operations implemented in child classes. ![]() As the queue is an interface, it contains only abstract methods and no data members.Note that these two implementations are not thread-safe, and for this, Java provides another implementation named PriorityBlockingQueue, which is threaded-safe.The PriorityQueue maintains the natural order of inserted elements. The LinkedList holds the elements as the standard of LinkedList, i.e., in insertion order.The implementations such as LinkedList and PriorityQueue implement the queue-specific methods declared in the Queue interface.As stated earlier, the Queue interface extends the collection interface hence, it supports all basic operational methods available in it.They are LinkedList and PriorityQueue.Ī queue can be declared as below: Queue q = new LinkedList() Queue q = new PriorityQueue() How does queue work in Java? Java has multiple implementations of the Queue interface, which we can use while using the Queues. The declaration shows that the queue accepts values as generic similar to collections, and we can pass any object to it. The queue is an interface, not a class, so it cannot be instantiated directly.
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