Java如何固定大小的线程池

public class TaskPool{
    private final ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newFixedThreadPool(9); // 创建一个大小为9的固定线程池，可以按照CPU的核数初步判定，如果CPU密集性任务则创建N+1个，如果是io密集型任务则创建2N+1个，其中N即CPU的核数
    protected void shutdown(){
        // do something
        // 这个方法等待线程池中所有已提交任务执行结束，不接收新任务，然后结束
        executor.shutdown(); 
        // 这个强制结束所有任务，然后正在等在的任务列表
        // executor.shutdownNow(); 
    }
    protected void execute(Runnable command){
        // do something
        // 提交任务
        executor.execute(command); 
    }
    public void status(){
        StringBuffer sb = new StringBuffer();
        // 当前正在执行任务的线程数
        sb.append(executor.getActiveCount() + "\n"); 
        // 当前正在等待执行的线程数
        sb.append(executor.getQueue().size() + "\n"); 
        // 返回已经完成的线程数
        sb.append(executor.getCompletedTaskCount() + "\n"); 
        System.out.println(sb.toString());
        // 注：以上方法都是返回一个大概值，因为线程在执行中，这些状态随时都会改变
    }
}       

public class Launcher{
    private TaskPool taskPool = new TaskPool();
    public static void main(String[] args){
        // 新建100个任务，Runnable的实现类Task
        Task[] tasks = new Task[100];
        for (int i = 0; i < tasks.length; i++){
            tasks[i] = new Task("Task " + (i+1));
            // 提交到线程池运行
            taskPool.execute(task[i]);
            if ( i % 50 == 0){
                taskPool.status();
        } 
    }
    private static class Task implements Runnable{
        private String name;
        public Task(String name){
            this.name = name;
        }
        public void run(){
            // do something
            System.out.println("我的名字是：" + this.name);
        }
    }
}

ExecutorService pool = Executors.newFixedThreadPool(2);
Runnable task = new Runnable() {
@Override
public void run() {
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
}
}
};
pool.execute(task);
pool.execute(task);
pool.execute(task);//线程池的带下只有两个 现在这个任务在其等待队列中排队等候

ExecutorService pool = Executors.newCachedThreadPool();
Runnable task = new Runnable() {
@Override
public void run() {
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
}
}
};
pool.execute(task);
pool.execute(task);
pool.execute(task);

ExecutorService pool = Executors.newSingleThreadExecutor();
Runnable task = new Runnable() {
@Override
public void run() {
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
}
}
};
pool.execute(task);
pool.execute(task);
pool.execute(task);

ScheduledExecutorService threadPool = Executors.newScheduledThreadPool(2);
Runnable task = new Runnable() {
@Override
public void run() {
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
}
}
};
threadPool.schedule(task, 2000, TimeUnit.MILLISECONDS);