Java队列接口 _Java队列接口

Java Queue接口以FIFO（先进先出）的方式对元素进行排序。在FIFO中, 首先删除第一个元素, 最后删除最后一个元素。
队列接口声明

public interface Queue< E> extends Collection< E>

Java队列接口方法

方法	描述
boolean add(object)	它用于将指定的元素插入此队列, 并在成功后返回true。
boolean offer(object)	用于将指定的元素插入此队列。
Object remove()	它用于检索和删除此队列的头部。
Object poll()	它用于检索和删除此队列的开头, 如果此队列为空, 则返回null。
Object element()	它用于检索但不删除此队列的头。
Object peek()	它用于检索但不删除此队列的头部, 如果此队列为空, 则返回null。

PriorityQueue类PriorityQueue类提供使用队列的便利。但是它不会以FIFO方式对元素进行排序。它继承了AbstractQueue类。
PriorityQueue类声明
我们来看一下java.util.PriorityQueue类的声明。

public class PriorityQueue< E> extends AbstractQueue< E> implements Serializable

Java PriorityQueue示例

import java.util.*; class TestCollection12{ public static void main(String args[]){ PriorityQueue< String> queue=new PriorityQueue< String> (); queue.add("Amit"); queue.add("Vijay"); queue.add("Karan"); queue.add("Jai"); queue.add("Rahul"); System.out.println("head:"+queue.element()); System.out.println("head:"+queue.peek()); System.out.println("iterating the queue elements:"); Iterator itr=queue.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } queue.remove(); queue.poll(); System.out.println("after removing two elements:"); Iterator< String> itr2=queue.iterator(); while(itr2.hasNext()){ System.out.println(itr2.next()); } } }

立即测试

Output:head:Amit head:Amit iterating the queue elements: Amit Jai Karan Vijay Rahul after removing two elements: Karan Rahul Vijay

Java PriorityQueue示例：书籍
【Java队列接口】让我们看一个PriorityQueue示例, 其中我们将书添加到队列中并打印所有书。 PriorityQueue中的元素必须为Comparable类型。默认情况下, String和Wrapper类是可比较的。要在PriorityQueue中添加用户定义的对象, 你需要实现Comparable接口。

import java.util.*; class Book implements Comparable< Book> { int id; String name, author, publisher; int quantity; public Book(int id, String name, String author, String publisher, int quantity) { this.id = id; this.name = name; this.author = author; this.publisher = publisher; this.quantity = quantity; } public int compareTo(Book b) { if(id> b.id){ return 1; }else if(id< b.id){ return -1; }else{ return 0; } } } public class LinkedListExample { public static void main(String[] args) { Queue< Book> queue=new PriorityQueue< Book> (); //Creating Books Book b1=new Book(121, "Let us C", "Yashwant Kanetkar", "BPB", 8); Book b2=new Book(233, "Operating System", "Galvin", "Wiley", 6); Book b3=new Book(101, "Data Communications & Networking", "Forouzan", "Mc Graw Hill", 4); //Adding Books to the queue queue.add(b1); queue.add(b2); queue.add(b3); System.out.println("Traversing the queue elements:"); //Traversing queue elements for(Book b:queue){ System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity); } queue.remove(); System.out.println("After removing one book record:"); for(Book b:queue){ System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity); } } }

输出：

Traversing the queue elements: 101 Data Communications & Networking Forouzan Mc Graw Hill 4 233 Operating System Galvin Wiley 6 121 Let us C Yashwant Kanetkar BPB 8 After removing one book record: 121 Let us C Yashwant Kanetkar BPB 8 233 Operating System Galvin Wiley 6