线性表数据结构解读（四）队列结构Queue

在上一篇文章中，我们详细介绍了栈结构，并结合Stack源码进行了分析，相关文章大家可以点击这里回看我的博客：线性表数据结构解读（三）栈结构Stack

队列的定义

队列是一种插入和删除分别在两端进行操作的线性表，一端进行插入操作，一端进行删除操作。

队列的特点

我们把进入队列端称为队列的对尾，用rear表示；离开队列的一端成为队列的头，用front表示，即在队列的头进行删除操作。

满队列

当一个队列rear指向最后一个位置时，不能够再进行插入操作，成为满队列状态。

空队列

当front的位置在rear后面时，表示队列中没有元素可以离开，说明队列是空状态。

循环队列

队列的头尾详解的顺讯存储结构称为循环队列

队列的缺点

队列空和满都可能出现假空和假满的状态

栈的存储结构

● 顺序队列

队列在顺序存储结构下所得到的结构，成为顺序队列。顺序栈类类似于数组，因此可以使用数组实现顺序栈的相关运算。

● 链式队列

队列在链式存储结构下所得到的结构，称为链队。链式队列类似于指针，在java中可以通过类的对象引用实现指针运算。



在Android中，我们常见具有代表性的队列结构为Queue，但是Queue确是一个接口，具体源码如下。

public interface Queue<E> extends Collection<E> {
/**
* 添加方法
* Inserts the specified element into this queue if it is possible to do so
* immediately without violating capacity restrictions, returning
* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
* if no space is currently available.
* @param e the element to add
* @return <tt>true</tt> (as specified by {@link Collection#add})
* @throws IllegalStateException if the element cannot be added at this
*         time due to capacity restrictions
* @throws ClassCastException if the class of the specified element
*         prevents it from being added to this queue
* @throws NullPointerException if the specified element is null and
*         this queue does not permit null elements
* @throws IllegalArgumentException if some property of this element
*         prevents it from being added to this queue
*/
boolean add(E e);

/**
* 入队方法
* 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.
* @param e the element to add
* @return <tt>true</tt> if the element was added to this queue, else
*         <tt>false</tt>
* @throws ClassCastException if the class of the specified element
*         prevents it from being added to this queue
* @throws NullPointerException if the specified element is null and
*         this queue does not permit null elements
* @throws IllegalArgumentException if some property of this element
*         prevents it from being added to this queue
*/
boolean offer(E e);

/**
* 移除元素方法
* 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.
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E remove();

/**
* 出队方法
* Retrieves and removes the head of this queue,
* or returns <tt>null</tt> if this queue is empty.
* @return the head of this queue, or <tt>null</tt> if this queue is empty
*/
E poll();

/**
* 获取某一个元素方法
* 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.
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E element();

/**
* 出队并删除掉
* Retrieves, but does not remove, the head of this queue,
* or returns <tt>null</tt> if this queue is empty.
* @return the head of this queue, or <tt>null</tt> if this queue is empty
*/
E peek();
}

既然是接口，那么就有实现类，我之前给大家分析的LinkedList源码正是实现了该接口，具体可以查阅我之前的博客线性表数据结构解读（二）链式存储结构LinkedList