public interface ThreadPool<Job extends Runnable>{  //執(zhí)行一個任務(wù)(Job),這個Job必須實現(xiàn)Runnable  void execute(Job job); //關(guān)閉線程池 void shutdown(); //增加工作者線程，即用來執(zhí)行任務(wù)的線程 void addWorkers(int num); //減少工作者線程 void removeWorker(int num); //獲取正在等待執(zhí)行的任務(wù)數(shù)量 void getJobSize();}

public class DefaultThreadPool<Job extends Runnable> implements ThreadPool<Job>{  // 線程池維護(hù)工作者線程的最大數(shù)量  private static final int MAX_WORKER_NUMBERS = 10;  // 線程池維護(hù)工作者線程的默認(rèn)值  private static final int DEFAULT_WORKER_NUMBERS = 5;  // 線程池維護(hù)工作者線程的最小數(shù)量  private static final int MIN_WORKER_NUMBERS = 1;  // 維護(hù)一個工作列表,里面加入客戶端發(fā)起的工作  private final LinkedList<Job> jobs = new LinkedList<Job>();  // 工作者線程的列表  private final List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());  // 工作者線程的數(shù)量  private int workerNum;  // 每個工作者線程編號生成  private AtomicLong threadNum = new AtomicLong(); //生成線程池public DefaultThreadPool() {    this.workerNum = DEFAULT_WORKER_NUMBERS;    initializeWorkers(this.workerNum);  }  public DefaultThreadPool(int num) {    if (num > MAX_WORKER_NUMBERS) {      this.workerNum =DEFAULT_WORKER_NUMBERS;    } else {      this.workerNum = num;    }    initializeWorkers(this.workerNum);  }//初始化每個工作者線程private void initializeWorkers(int num) {    for (int i = 0; i < num; i++) {      Worker worker = new Worker();      //添加到工作者線程的列表      workers.add(worker);      //啟動工作者線程      Thread thread = new Thread(worker);      thread.start();    }  }public void execute(Job job) {    if (job != null) {    //根據(jù)線程的"等待/通知機(jī)制"這里必須對jobs加鎖      synchronized (jobs) {        jobs.addLast(job);        jobs.notify();      }    }  }  //關(guān)閉線程池即關(guān)閉每個工作者線程   public void shutdown() {    for (Worker w : workers) {      w.shutdown();    }  }   //增加工作者線程    public void addWorkers(int num) {    //加鎖，防止該線程還么增加完成而下個線程繼續(xù)增加導(dǎo)致工作者線程超過最大值    synchronized (jobs) {      if (num + this.workerNum > MAX_WORKER_NUMBERS) {        num = MAX_WORKER_NUMBERS - this.workerNum;      }      initializeWorkers(num);      this.workerNum += num;    }  }  //減少工作者線程public void removeWorker(int num) {    synchronized (jobs) {    if(num>=this.workerNum){         throw new IllegalArgumentException("超過了已有的線程數(shù)量");         }      for (int i = 0; i < num; i++) {        Worker worker = workers.get(i);        if (worker != null) {        //關(guān)閉該線程并從列表中移除          worker.shutdown();          workers.remove(i);        }      }      this.workerNum -= num;    }  }public int getJobSize() {    // TODO Auto-generated method stub    return workers.size();  }//定義工作者線程class Worker implements Runnable {    // 表示是否運(yùn)行該worker    private volatile boolean running = true;    public void run() {      while (running) {        Job job = null;        //線程的等待/通知機(jī)制        synchronized (jobs) {          if (jobs.isEmpty()) {            try {              jobs.wait();//線程等待喚醒            } catch (InterruptedException e) {              //感知到外部對該線程的中斷操作，返回              Thread.currentThread().interrupt();              return;            }          }          // 取出一個job          job = jobs.removeFirst();        }        //執(zhí)行job        if (job != null) {          job.run();        }      }    }    // 終止該線程    public void shutdown() {      running = false;    }  }}