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Java queue pop last element12/1/2023 There are two common ways to implement a queue: using a list or using the queue class from the built-in queue module. Print("Processing task:", task, "with priority:", priority) # Add tasks to the priority queue with their priority My_priority_queue = queue.PriorityQueue() Python’s queue module provides an implementation of the Priority Queue data structure. The element with the highest priority is dequeued first, followed by the element with the second highest priority, and so on. # The two items are removed from the queueĪ Priority Queue is a special type of queue where each element has a priority assigned to it, and the elements are dequeued in order of their priority. # The oldest item is removed from the queue You can dequeue elements using the front pointer and enqueue elements using the rear pointer in a circular queue. In a circular queue, there are two pointers, front and rear. This type of queue is useful when we want to store data in a circular manner and treat the data structure as a circular list. In other words, a circular queue wraps around and reuses the space that the first element took up after the last element. Print(my_deque) # deque()Ĭircular Queue is a type of queue in which the last element is connected to the first element to make a circular data structure. # Remove a item from the back of the deque # Remove a item from the front of the deque # Add a new item to the back of the deque # Add a new item to the front of the deque Instead of empty(), you have to call isEmpty().My_deque = deque().We have the methods push(), pop(), and peek().The interface is similar to that of Stack: Instead, the Java developers recommend using one of the Deque implementations, such as ArrayDeque. Better is usually optimistic locking by CAS ("compare-and-swap") operations as found in the concurrent queue and deque implementations. Using synchronized on every method call is not a particularly performant means of making a data structure thread-safe.So by using Stack, you are committing to a specific implementation. Stack does not implement an interface.By extending Vector, Stack provides operations that have no place in a stack, such as accessing elements by their index or inserting and deleting elements at arbitrary positions.What exactly does this mean? In my opinion, Stack should not be used for the following reasons: "A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class." The Java developers recommend not to use anymore. Just like pop(), also peek() would throw an EmptyStackException if the stack is empty. What happens if we call pop() one more time? ( "stack.pop() = " + stack.pop()) Code language: Java ( java )Īs the stack is now empty, an EmptyStackException is thrown: Exception in thread "main" Īt java.base/(Stack.java:101)Īt java.base/(Stack.java:83)Īt eu.main(JavaStackDemo.java:28) Code language: plaintext ( plaintext ) Stack.pop() = apple Code language: plaintext ( plaintext ) We see that the elements are retrieved in reverse order: stack.pop() = pear ( "stack.pop() = " + stack.pop()) Code language: Java ( java ) We take out the three elements again: ( "stack.pop() = " + stack.pop()) That's because we pushed two more elements onto the stack after "apple". This means that "apple" is in the third position of the stack. The output is: arch("apple") = 3 Code language: plaintext ( plaintext ) Using search(), we can look for an element: ( "arch(\"apple\") = " + arch( "apple")) Code language: Java ( java ) The last inserted element, "pear", is at the top of the stack. So Stack's toString() method prints the elements from bottom to top. ( "stack.empty() = " + stack.empty()) Code language: Java ( java ) Stack.push( "pear") Code language: Java ( java )Īfter that, we print the stack's contents – and the results of peek() and empty() – to the console: ( "stack = " + stack) The following code snippets show an example use of Stack (you can find the complete code in the JavaStackDemo class in the GitHub repo).įirst, we create a stack and put the elements "apple", "orange", and "pear" on the stack using push(): Stack stack = new Stack() Just like Vector, Stack is thread-safe: all methods are synchronized. I show how the methods work in the following example.
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