【Java并发编程】3、DelayQueue应用场景，多考生考试

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。

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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();         }     }   }