Java 线程池和普通线程区别

Java 中线程池和原生线程貌似有点不一样，求解答。。。
下面附上两个 Demo 完成的功能是主线程等待所有子线程结束然后统计总耗时，第一个使用了线程池，第二个使用 Java 原生线程。

示例一：

import java.util.LinkedList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* Created on 2016/11/25 * * @author annpeter.it@gmail.com
*/public class Bootstrap {
 private static ExecutorService executorService = Executors.newFixedThreadPool(10);
private static List list = new LinkedList<>();
private static Random random = new Random();

public static void main(String[] args) throws InterruptedException {
     long from = System.currentTimeMillis();

for (int i = 0; i < 10; i++) {
         final int index = i;
Runnable runnable = () -> {
             try {
                 int time = random.nextInt(5000);
Thread.sleep(time);
System.out.println("i = " + index + " sleep: " + time);
} catch (InterruptedException ignored) {
                 // passed
}
         };

Thread thread = new Thread(runnable);

executorService.execute(thread);
list.add(thread);
}

     for (Thread thread : list) {
         System.out.println(thread.isAlive());
thread.join();
}

     long to = System.currentTimeMillis();
System.out.println("总用时： " + (to - from) );
}
}

示例二：

import java.util.LinkedList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* Created on 2016/11/25 * * @author annpeter.it@gmail.com
*/public class Bootstrap {
  private static List list = new LinkedList<>();
private static Random random = new Random();

public static void main(String[] args) throws InterruptedException {
      long from = System.currentTimeMillis();

for (int i = 0; i < 10; i++) {
          final int index = i;
Runnable runnable = () -> {
              try {
                  int time = random.nextInt(5000);
Thread.sleep(time);
System.out.println("i = " + index + " sleep: " + time);
} catch (InterruptedException ignored) {
                  // passed
}
          };

Thread thread = new Thread(runnable);
thread.start();
list.add(thread);
}

      for (Thread thread : list) {
          System.out.println(thread.isAlive());
thread.join();
}

      long to = System.currentTimeMillis();
System.out.println("总用时： " + (to - from) );
}
}