Структура данных queue java
Interface Queue
- Type Parameters: E — the type of elements held in this collection All Superinterfaces: Collection, IterableAll Known Subinterfaces: BlockingDeque, BlockingQueue, Deque, TransferQueueAll Known Implementing Classes: AbstractQueue, ArrayBlockingQueue, ArrayDeque, ConcurrentLinkedDeque, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingDeque, LinkedBlockingQueue, LinkedList, LinkedTransferQueue, PriorityBlockingQueue, PriorityQueue, SynchronousQueue
A collection designed for holding elements prior to processing. Besides basic Collection operations, queues provide additional insertion, extraction, and inspection operations. Each of these methods exists in two forms: one throws an exception if the operation fails, the other returns a special value (either null or false , depending on the operation). The latter form of the insert operation is designed specifically for use with capacity-restricted Queue implementations; in most implementations, insert operations cannot fail.
| Throws exception | Returns special value | |
| Insert | add(e) | offer(e) |
| Remove | remove() | poll() |
| Examine | element() | peek() |
Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues, which order elements according to a supplied comparator, or the elements’ natural ordering, and LIFO queues (or stacks) which order the elements LIFO (last-in-first-out). Whatever the ordering used, the head of the queue is that element which would be removed by a call to remove() or poll() . In a FIFO queue, all new elements are inserted at the tail of the queue. Other kinds of queues may use different placement rules. Every Queue implementation must specify its ordering properties. The offer method inserts an element if possible, otherwise returning false . This differs from the Collection.add method, which can fail to add an element only by throwing an unchecked exception. The offer method is designed for use when failure is a normal, rather than exceptional occurrence, for example, in fixed-capacity (or «bounded») queues. The remove() and poll() methods remove and return the head of the queue. Exactly which element is removed from the queue is a function of the queue’s ordering policy, which differs from implementation to implementation. The remove() and poll() methods differ only in their behavior when the queue is empty: the remove() method throws an exception, while the poll() method returns null . The element() and peek() methods return, but do not remove, the head of the queue. The Queue interface does not define the blocking queue methods, which are common in concurrent programming. These methods, which wait for elements to appear or for space to become available, are defined in the BlockingQueue interface, which extends this interface. Queue implementations generally do not allow insertion of null elements, although some implementations, such as LinkedList , do not prohibit insertion of null . Even in the implementations that permit it, null should not be inserted into a Queue , as null is also used as a special return value by the poll method to indicate that the queue contains no elements. Queue implementations generally do not define element-based versions of methods equals and hashCode but instead inherit the identity based versions from class Object , because element-based equality is not always well-defined for queues with the same elements but different ordering properties. This interface is a member of the Java Collections Framework.
Method Summary
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
Interface Queue
Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues, which order elements according to a supplied comparator, or the elements’ natural ordering, and LIFO queues (or stacks) which order the elements LIFO (last-in-first-out). Whatever the ordering used, the head of the queue is that element which would be removed by a call to remove() or poll() . In a FIFO queue, all new elements are inserted at the tail of the queue. Other kinds of queues may use different placement rules. Every Queue implementation must specify its ordering properties.
The offer method inserts an element if possible, otherwise returning false . This differs from the Collection.add method, which can fail to add an element only by throwing an unchecked exception. The offer method is designed for use when failure is a normal, rather than exceptional occurrence, for example, in fixed-capacity (or «bounded») queues.
The remove() and poll() methods remove and return the head of the queue. Exactly which element is removed from the queue is a function of the queue’s ordering policy, which differs from implementation to implementation. The remove() and poll() methods differ only in their behavior when the queue is empty: the remove() method throws an exception, while the poll() method returns null .
The element() and peek() methods return, but do not remove, the head of the queue.
The Queue interface does not define the blocking queue methods, which are common in concurrent programming. These methods, which wait for elements to appear or for space to become available, are defined in the BlockingQueue interface, which extends this interface.
Queue implementations generally do not allow insertion of null elements, although some implementations, such as LinkedList , do not prohibit insertion of null . Even in the implementations that permit it, null should not be inserted into a Queue , as null is also used as a special return value by the poll method to indicate that the queue contains no elements.
Queue implementations generally do not define element-based versions of methods equals and hashCode but instead inherit the identity based versions from class Object , because element-based equality is not always well-defined for queues with the same elements but different ordering properties.
This interface is a member of the Java Collections Framework.
Структура данных queue java
Interface Queue
- Type Parameters: E — the type of elements held in this queue All Superinterfaces: Collection, IterableAll Known Subinterfaces: BlockingDeque, BlockingQueue, Deque, TransferQueueAll Known Implementing Classes: AbstractQueue , ArrayBlockingQueue , ArrayDeque , ConcurrentLinkedDeque , ConcurrentLinkedQueue , DelayQueue , LinkedBlockingDeque , LinkedBlockingQueue , LinkedList , LinkedTransferQueue , PriorityBlockingQueue , PriorityQueue , SynchronousQueue
A collection designed for holding elements prior to processing. Besides basic Collection operations, queues provide additional insertion, extraction, and inspection operations. Each of these methods exists in two forms: one throws an exception if the operation fails, the other returns a special value (either null or false , depending on the operation). The latter form of the insert operation is designed specifically for use with capacity-restricted Queue implementations; in most implementations, insert operations cannot fail.
| Throws exception | Returns special value | |
|---|---|---|
| Insert | add(e) | offer(e) |
| Remove | remove() | poll() |
| Examine | element() | peek() |
Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues, which order elements according to a supplied comparator, or the elements’ natural ordering, and LIFO queues (or stacks) which order the elements LIFO (last-in-first-out). Whatever the ordering used, the head of the queue is that element which would be removed by a call to remove() or poll() . In a FIFO queue, all new elements are inserted at the tail of the queue. Other kinds of queues may use different placement rules. Every Queue implementation must specify its ordering properties. The offer method inserts an element if possible, otherwise returning false . This differs from the Collection.add method, which can fail to add an element only by throwing an unchecked exception. The offer method is designed for use when failure is a normal, rather than exceptional occurrence, for example, in fixed-capacity (or «bounded») queues. The remove() and poll() methods remove and return the head of the queue. Exactly which element is removed from the queue is a function of the queue’s ordering policy, which differs from implementation to implementation. The remove() and poll() methods differ only in their behavior when the queue is empty: the remove() method throws an exception, while the poll() method returns null . The element() and peek() methods return, but do not remove, the head of the queue. The Queue interface does not define the blocking queue methods, which are common in concurrent programming. These methods, which wait for elements to appear or for space to become available, are defined in the BlockingQueue interface, which extends this interface. Queue implementations generally do not allow insertion of null elements, although some implementations, such as LinkedList , do not prohibit insertion of null . Even in the implementations that permit it, null should not be inserted into a Queue , as null is also used as a special return value by the poll method to indicate that the queue contains no elements. Queue implementations generally do not define element-based versions of methods equals and hashCode but instead inherit the identity based versions from class Object , because element-based equality is not always well-defined for queues with the same elements but different ordering properties. This interface is a member of the Java Collections Framework.
Method Summary
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
Queue Implementations
The Queue implementations are grouped into general-purpose and concurrent implementations.
General-Purpose Queue Implementations
As mentioned in the previous section, LinkedList implements the Queue interface, providing first in, first out (FIFO) queue operations for add , poll , and so on.
The PriorityQueue class is a priority queue based on the heap data structure. This queue orders elements according to the order specified at construction time, which can be the elements’ natural ordering or the ordering imposed by an explicit Comparator .
The queue retrieval operations poll , remove , peek , and element access the element at the head of the queue. The head of the queue is the least element with respect to the specified ordering. If multiple elements are tied for least value, the head is one of those elements; ties are broken arbitrarily.
PriorityQueue and its iterator implement all of the optional methods of the Collection and Iterator interfaces. The iterator provided in method iterator is not guaranteed to traverse the elements of the PriorityQueue in any particular order. For ordered traversal, consider using Arrays.sort(pq.toArray()) .
Concurrent Queue Implementations
The java.util.concurrent package contains a set of synchronized Queue interfaces and classes. BlockingQueue extends Queue with operations that wait for the queue to become nonempty when retrieving an element and for space to become available in the queue when storing an element. This interface is implemented by the following classes:
- LinkedBlockingQueue an optionally bounded FIFO blocking queue backed by linked nodes
- ArrayBlockingQueue a bounded FIFO blocking queue backed by an array
- PriorityBlockingQueue an unbounded blocking priority queue backed by a heap
- DelayQueue a time-based scheduling queue backed by a heap
- SynchronousQueue a simple rendezvous mechanism that uses the BlockingQueue interface
In JDK 7, TransferQueue is a specialized BlockingQueue in which code that adds an element to the queue has the option of waiting (blocking) for code in another thread to retrieve the element. TransferQueue has a single implementation: