Queue翻译

翻译

类注释

A collection designed for holding elements prior to processing.
一个设计用来保存需要预先处理元素的Collection

Besides basic {@link java.util.Collection Collection} operations,
queues provide additional insertion, extraction, and inspection
operations.  
除了基本的 Collection操作,队列提供额外的插入、提取和检验操作

Each of these methods exists in two forms: one throws
an exception if the operation fails, the other returns a special
value (either {@code null} or {@code false}, depending on the
operation).  

这些方法中存在两种形式:
一个抛出一个异常,如果操作失败, 
另一个返回一个特殊的值( null或者 false,根据操作)


The latter form of the insert operation is designed
specifically for use with capacity-restricted {@code Queue}
implementations; 

后者的插入操作形式是专门为使用容量限制 Queue实现;

in most implementations, insert operations cannot  fail.

在大多数实现,insert操作不能失败。

六个主要方法

method	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. 

队列通常,但不一定,顺序元素FIFO(先进先出)的方式

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).

例如在优先队列中,顺序元素根据提供的比较器,或者元素的自然顺序,后进先出队列顺序(或堆栈)后进先出的元素。
   
Whatever the ordering used, the <em>head</em> of the queue is that
element which would be removed by a call to {@link #remove() } or
{@link #poll()}.  In a FIFO queue, all new elements are inserted at
the <em>tail</em> of the queue. Other kinds of queues may use
different placement rules.  Every {@code Queue} implementation
must specify its ordering properties.

无论使用哪种顺序,队列的头部是元素将被调用remove()或poll()。在FIFO队列,所有新元素插入到队列的尾部。
其他类型的队列可能使用不同的放置规则。每个Queue实现必须指定其排序属性。

The {@link #offer offer} method inserts an element if possible,
otherwise returning {@code false}.  This differs from the {@link
java.util.Collection#add Collection.add} method, which can fail to
add an element only by throwing an unchecked exception.  The
{@code offer} method is designed for use when failure is a normal,
rather than exceptional occurrence, for example, in fixed-capacity
(or &quot;bounded&quot;) queues.

offer方法插入一个元素如果可能,否则返回false。
这不同于Collection.add方法,它可以不添加一个元素只有抛出未检测的异常。
offer方法是设计用于当失败是正常的,而不是特殊情况,例如,在固定电容(或“有界”)队列。


The {@link #remove()} and {@link #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 {@code remove()} and
{@code poll()} methods differ only in their behavior when the
queue is empty: the {@code remove()} method throws an exception,
while the {@code poll()} method returns {@code null}.
 

remove()和poll()方法删除并返回队列的头部。从队列中删除哪些元素是一个函数队列的排序策略,这不同于实现来实现。
remove()和poll()方法不同队列为空时:remove()方法抛出一个异常,而poll()方法返回null。

The {@link #element()} and {@link #peek()} methods return, but do
not remove, the head of the queue.
element() peek()方法返回,但不要删除队列的头部。

The {@code Queue} interface does not define the <i>blocking queue
methods</i>, which are common in concurrent programming.  These methods,
which wait for elements to appear or for space to become available, are
defined in the {@link java.util.concurrent.BlockingQueue} interface, which
extends this interface.

Queue接口没有定义阻塞队列的方法,常见的并发编程。
这些方法,等待元素出现或空间可用BlockingQueue接口中定义,扩展这个接口。

{@code Queue} implementations generally do not allow insertion
of {@code null} elements, although some implementations, such as
{@link LinkedList}, do not prohibit insertion of {@code null}.
Even in the implementations that permit it, {@code null} should
not be inserted into a {@code Queue}, as {@code null} is also
used as a special return value by the {@code poll} method to
indicate that the queue contains no elements.

Queue null元素的实现通常不允许插入,尽管一些实现,如LinkedList、不禁止插入null。
即使在允许它的实现,null不应插入一个Queue null也用作特殊poll返回值的方法表明,队列中不包含任何元素。

{@code Queue} implementations generally do not define
element-based versions of methods {@code equals} and
{@code hashCode} but instead inherit the identity based versions
from class {@code Object}, because element-based equality is not
always well-defined for queues with the same elements but different
ordering properties.

Queue实现通常不定义的元素版本方法equals hashCode而是继承类Object的基于身份的版本,
因为元素相同的平等并不总是明确的队列元素但不同排序属性。

源码

public interface Queue<E> extends Collection<E> {
	/**
	 * Inserts the specified element into this queue if it is possible to do so
	 * immediately without violating capacity restrictions, returning
	 * {@code true} upon success and throwing an {@code IllegalStateException}
	 * if no space is currently available.
	 * 将指定的元素插入此队列能否立即这样做,在不违反容量限制,返回 true成功
	   和抛出 IllegalStateException如果没有目前可用的空间
	 */
	boolean add(E e);

	/**
	 * Inserts the specified element into this queue if it is possible to do
	 * so immediately without violating capacity restrictions.
	 * When using a capacity-restricted queue, this method is generally
	 * preferable to {@link #add}, which can fail to insert an element only
	 * by throwing an exception.
	 * 将指定的元素插入此队列能否立即这样做,在不违反容量限制。
	   使用capacity-restricted队列时,这种方法通常比 add(E),无法插入一个元素只有通过抛出异常。
	 */
	boolean offer(E e);

	/**
	 * Retrieves and removes the head of this queue.  This method differs
	 * from {@link #poll poll} only in that it throws an exception if this
	 * queue is empty.
	 * 检索并删除此队列的头。这个方法与 poll唯一的不同之处在于,它将抛出一个异常,如果这个队列是空的。
	 */
	E remove();

	/**
	 * Retrieves and removes the head of this queue,
	 * or returns {@code null} if this queue is empty.
	 * 检索并删除此队列的头,或者返回 null如果这个队列是空的。
	 */
	E poll();

	/**
	 * Retrieves, but does not remove, the head of this queue.  This method
	 * differs from {@link #peek peek} only in that it throws an exception
	 * if this queue is empty.
	 * 检索,但不删除此队列的头。这个方法与 peek唯一的不同之处在于,它将抛出一个异常,如果这个队列是空的。
	 */
	E element();

	/**
	 * Retrieves, but does not remove, the head of this queue,
	 * or returns {@code null} if this queue is empty.
	 * 检索,但不删除此队列的头,或者返回 null如果这个队列是空的。
	 */
	E peek();
}

总结

1. 队列是什么？就是用来装一组元素的集合
2. 队列并不都是FIFO
3. 队列并不提供阻塞（由子类实现)
4. 队列可以指定容量
5. 一类抛异常一类为不抛