Java线程面试题：什么是线程池？为什么要使用线程池？

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolDemo {
    public static void main(String[] args) {
        // 创建一个可重用、固定线程数的线程池
        ExecutorService threadPool = Executors.newFixedThreadPool(3);
        // 向线程池中添加 10 个任务
        for (int i = 0; i < 10; i++) {
            Runnable task = new Task(i);
            threadPool.execute(task);
        }
        // 禁止提交新任务，并试图终止所有正在执行的任务
        threadPool.shutdown();
        // 判断是否所有任务都已经执行完成
        while (!threadPool.isTerminated()) {
            Thread.yield();
        }
        System.out.println("All tasks are completed.");
    }
}
class Task implements Runnable {
    private int number;
    public Task(int number) {
        this.number = number;
    }
    @Override
    public void run() {
        System.out.println("Task " + number + " is running on thread " + Thread.currentThread().getName());
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Task " + number + " is completed on thread " + Thread.currentThread().getName());
    }
}