Queue Interfaces
The java.util.Queue interface defines the queue data structure, which stores elements in the order in which they are inserted. New additions go to the end of the line, and elements are removed from the front. It creates a first-in first-out system. This interface is implemented by java.util.LinkedList, java.util.ArrayDeque, and java.util.PriorityQueue. LinkedList, of course, also implements the List interface and can also be used as one. But it also has the Queue methods. ArrayDeque implements the queue as an array. Both LinkedList and ArrayDeque also implement the java.util.Deque interface, giving it more flexibility.
java.util.Queue can be used more flexibly with its subinterface, java.util.BlockingQueue. The BlockingQueue interface works like a regular queue, but additions to and removals from the queue are blocking. If remove is called on an empty queue, it can be set to wait either a specified time or indefinitely for an item to appear in the queue. Similarly, adding an item is subject to an optional capacity restriction on the queue, and the method can wait for space to become available in the queue before returning.
The java.util.Queue interface is expanded by the java.util.Deque subinterface. Deque creates a double-ended queue. While a regular queue only allows insertions at the rear and removals at the front, the deque allows insertions or removals to take place both at the front and the back. A deque is like a queue that can be used forwards or backwards, or both at once. Additionally, both a forwards and a backwards iterator can be generated. The Deque interface is implemented by java.util.ArrayDeque and java.util.LinkedList.
The java.util.concurrent.BlockingDeque interface works similarly to java.util.concurrent.BlockingQueue. The same methods for insertion and removal with time limits for waiting for the insertion or removal to become possible are provided. However, the interface also provides the flexibility of a deque. Insertions and removals can take place at both ends. The blocking function is combined with the deque function.
Read more about this topic: Java Collections Framework
Famous quotes containing the word queue:
“English people apparently queue up as a sort of hobby. A family man might pass a mild autumn evening by taking the wife and kids to stand in the cinema queue for a while and then leading them over for a few minutes in the sweetshop queue and then, as a special treat for the kids, saying “Perhaps we’ve time to have a look at the Number Thirty-One bus queue before we turn in.””
—Calvin Trillin (b. 1940)