大家好，又见面了，我是你们的朋友全栈君。
项目github地址：bitcarmanlee easy-algorithm-interview-and-practice 欢迎大家star，留言，一起学习进步
1.队列的特点
队列是一种比较特殊的线性结构。它只允许在表的前端（front）进行删除操作，而在表的后端（rear）进行插入操作。进行插入操作的端称为队尾，进行删除操作的端称为队头。 队列中最先插入的元素也将最先被删除，对应的最后插入的元素将最后被删除。因此队列又称为“先进先出”（FIFO—first in first out）的线性表，与栈(FILO-first in last out)刚好相反。
2.java中的队列
java中的Queue接口就实现了队列的功能。
代码语言：javascript复制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.
*
* @param e the element to add
* @return {@code true} (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);
/**
* 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 {@code true} if the element was added to this queue, else
* {@code false}
* @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);
/**
* 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();
/**
* Retrieves and removes the head of this queue,
* or returns {@code null} if this queue is empty.
*
* @return the head of this queue, or {@code null} if this queue is empty
*/
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.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E element();
/**
* Retrieves, but does not remove, the head of this queue,
* or returns {@code null} if this queue is empty.
*
* @return the head of this queue, or {@code null} if this queue is empty
*/
E peek();
}不得不说，JDK里的代码以及注释看着就是很舒服。各位稍微花点时间看看JDK里的源码以及注释，相信会有很多收获。
3.测试Queue接口
JDK中,LinkedList类实现了Queue接口，可以当Queue使用。
代码语言：javascript复制public class QueueTest {
@Test
public void test() {
Queue<Integer> queue = new LinkedList<>();
queue.offer(1);
queue.offer(2);
queue.offer(3);
queue.offer(4);
for(int e : queue) {
System.out.println(e);
}
System.out.println("----------");
System.out.println("poll : " queue.poll());
System.out.println("----------");
for(int e : queue) {
System.out.println(e);
}
System.out.println("ele is: " queue.element());
System.out.println("----------");
for(int e : queue) {
System.out.println(e);
}
System.out.println("peek : " queue.peek());
System.out.println("----------");
for(int e : queue) {
System.out.println(e);
}
}
}最终代码运行的结果：
代码语言：javascript复制1
2
3
4
----------
poll : 1
----------
2
3
4
ele is: 2
----------
2
3
4
peek : 2
----------
2
3
4结合第二部分内容，可以有以下结论: 1.尽量使用offer()方法添加元素，使用poll()方法移除元素。dd()和remove()方法在失败的时候会抛出异常。 2.peek方法不会删除元素， Retrieves, but does not remove, the head of this queue,
发布者：全栈程序员栈长，转载请注明出处：https://javaforall.cn/159004.html原文链接：https://javaforall.cn
