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

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

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