对集合使用Comparator

import java.util.Comparator;
import java.util.PriorityQueue;

/**
 * 对集合使用Comparator，不改变对象的自然顺序
 * @author Administrator
 *
 */
public class PriMsgQDemo {
    public static void main(String[] args) {
        Message m;
        //自然顺序排列
        PriorityQueue<Message> pq = new PriorityQueue<Message>(3);
        
        pq.add(new Message("Message at main office at 3pm", Message.PLevel.Low));
        pq.add(new Message("Fire in warehouse!", Message.PLevel.High));
        pq.add(new Message("Report due Tuesday", Message.PLevel.Medium));
        
        System.out.println("Message in natural-order priority: ");
        while((m = pq.poll()) != null){
            System.out.println(m.msg+"Priority: " + m.priority);
        }
        System.out.println();
        //使用比较器
        PriorityQueue<Message> pqRev = new PriorityQueue<Message>(3, new RevMsgComparer());
        
        pqRev.add(new Message("Message at main office at 3pm", Message.PLevel.Low));
        pqRev.add(new Message("Fire in warehouse!", Message.PLevel.High));
        pqRev.add(new Message("Report due Tuesday", Message.PLevel.Medium));
        
        System.out.println("Message in reverse-order priority: ");
        while((m = pqRev.poll()) != null){
            System.out.println(m.msg+"Priority: " + m.priority);
        }
    }
}

class Message implements Comparable<Message>{

    String msg;
    enum PLevel {
        High, Medium, Low
    }
    
    PLevel priority;
    public Message(String str, PLevel pri) {
        msg = str;
        priority = pri;
    }
    
    @Override
    public int compareTo(Message o) {
        return priority.compareTo(o.priority);
    }
    
}

class RevMsgComparer implements Comparator<Message>{

    @Override
    public int compare(Message o1, Message o2) {
        return o2.priority.compareTo(o1.priority);
    }
    
}