A Queue is a data structure that holds a list of items in a particular order. The order is First In First Out, which means the first item that goes in is the first item that comes out. Think of it like a line at a store or a queue at a theme park ride.
In Java, the Queue interface is present in the java.util package and it extends the Collection interface. This means it can hold a collection of elements that are about to be processed in the FIFO order.
There are different implementations of a Queue in Java, including LinkedList and PriorityQueue, but it's important to note that these implementations are not thread-safe. If thread safety is needed, then the PriorityBlockingQueue is an alternative implementation to consider.
To create a Queue object in Java, you need to use a class that extends the Queue interface. Since Java 1.5, you can also create a type-safe queue by restricting the type of object that can be stored in the Queue.
When choosing between ArrayDeque and LinkedList in Java, ArrayDeque is generally preferred because it's faster and cache-friendly. While LinkedList has a time complexity of O(1) for adding and removing items in the worst-case scenario, ArrayDeque has an amortized time complexity of O(1). This means that for a few operations that require internal resizing of the array, the time of operation might increase to O(n) or linear time.
Some of the methods of the Queue interface include peek(), offer(), poll(), element(), add(), and remove(). These methods are used to view and add elements to the queue, as well as remove and retrieve them.
The Queue data structure has several applications in computer science, such as CPU scheduling, disk scheduling, web servers, routers, and data transfer between processes.
