【Java并发编程】3、DelayQueue应用场景，多考生考试

该场景来自于：http://www.cnblogs.com/sunzhenchao/p/3515085.html。

模拟一个考试的日子，考试时间为120分钟，30分钟后才可交卷，当时间到了，或学生都交完卷了考试结束。

这个场景中几个点需要注意：

1. 考试时间为120分钟，30分钟后才可交卷，初始化考生完成试卷时间最小应为30分钟
2. 对于能够在120分钟内交卷的考生，如何实现这些考生交卷
3. 对于120分钟内没有完成考试的考生，在120分钟考试时间到后需要让他们强制交卷
4. 在所有的考生都交完卷后，需要将控制线程关闭

抽象出两个类，学生类和老师类，用DelayQueue存储考生（Student类）。每一个考生都有自己的名字和完成试卷的时间

Teacher线程对DelayQueue进行监控，收取完成试卷小于120分钟的学生的试卷。当考试时间120分钟到时，teacher线程宣布考试结束，强制DelayQueue中还存在的考生交卷。

package zhongqiu.common.base.thread;

import java.util.Iterator;
import java.util.Random;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

public class DelayQueueDemoOne {

	public static void main(String[] args) throws InterruptedException {
		// TODO Auto-generated method stub
		int studentNumber = 20;
		DelayQueue<Student> students = new DelayQueue<Student>();
		Random random = new Random();
		for (int i = 0; i < studentNumber; i++) {
			students.put(new Student("student" + (i + 1), 30 + random.nextInt(120)));
		}
		students.put(new Student("student",120));
		Thread teacherThread = new Thread(new Teacher(students));
		teacherThread.start();
	}
}

class Student implements Runnable, Delayed {

	private String name;
	public long workTime;
	private long submitTime;
	private boolean isForce = false;

	public Student() {
	}

	public Student(String name, long workTime) {
		this.name = name;
		this.workTime = workTime;
		this.submitTime = TimeUnit.NANOSECONDS.convert(workTime, TimeUnit.NANOSECONDS) + System.nanoTime();// 纳秒级别
	}

	@Override
	public int compareTo(Delayed o) {
		// TODO Auto-generated method stub
		if (o == null || !(o instanceof Student))
			return 1;
		if (o == this)
			return 0;
		Student s = (Student) o;
		if (this.workTime > s.workTime) {
			return 1;
		} else if (this.workTime == s.workTime) {
			return 0;
		} else {
			return -1;
		}
	}

	@Override
	public long getDelay(TimeUnit unit) {
		// TODO Auto-generated method stub
		return unit.convert(submitTime - System.nanoTime(), TimeUnit.NANOSECONDS);
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		if (isForce) {
			System.out.println(name + " 交卷，实际用时 120分钟");
		} else {
			System.out.println(name + " 交卷," + "实际用时 " + workTime + " 分钟");
		}
	}

	public boolean isForce() {
		return isForce;
	}

	public void setForce(boolean isForce) {
		this.isForce = isForce;
	}

}

class Teacher implements Runnable {
	private int counter = 20;
	private DelayQueue<Student> students;

	public Teacher(DelayQueue<Student> students) {
		this.students = students;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		try {
			System.out.println(" test start");
			while (counter > 0) {
				Student student = students.poll();
				if (student.workTime<120) {
					student.run();
					if (counter > 0) {
						counter--;
					}
				} else {
					System.out.println(" 考试时间到，全部交卷！");
					Student tmpStudent;
					for (Iterator<Student> iterator2 = students.iterator(); iterator2.hasNext();) {
						tmpStudent = iterator2.next();
						tmpStudent.setForce(true);
						tmpStudent.run();
						if (counter > 0) {
							counter--;
						}
					}
				}
			}
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}

}