【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：

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

对于能够在120分钟内交卷的考生，如何实现这些考生交卷

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

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();
}
}

}