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队列接口的方法
| 方法 |
说明 |
| boolean add(object) |
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。 |
| Object poll() |
它用于检索和删除此队列的头部，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开头，如果此队列为空，则返回null。 |
PriorityQueue类
PriorityQueue类提供了使用队列的便利。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
让我们看看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());
}
}
}
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，在该示例中，我们将书籍添加到队列中并打印所有书籍。 PriorityQueue中的元素必须为Comparable类型。默认情况下，String和Wrapper类是Comparable的。要在PriorityQueue中添加用户定义的对象，您需要实现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>
();
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);
queue.add(b1);
queue.add(b2);
queue.add(b3);
System.out.println("Traversing the 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
