Java threadfactroy 创建线程

Java编程思想中的样列代码：

 package concurrency;

//: concurrency/CaptureUncaughtException.java
import java.util.concurrent.*;

class ExceptionThread2 implements Runnable {
  public void run() {
    Thread t = Thread.currentThread();
    System.out.println("run() by " + t);
    System.out.println(
      "eh = " + t.getUncaughtExceptionHandler());
    throw new RuntimeException();
  }
}

class MyUncaughtExceptionHandler implements
Thread.UncaughtExceptionHandler {
  public void uncaughtException(Thread t, Throwable e) {
    System.out.println("caught " + e);
  }
}

class HandlerThreadFactory implements ThreadFactory {
  public Thread newThread(Runnable r) {
    System.out.println(this + " creating new Thread");
    Thread t = new Thread(r);
    System.out.println("created " + t);
    t.setUncaughtExceptionHandler(
      new MyUncaughtExceptionHandler());
    System.out.println(
      "eh = " + t.getUncaughtExceptionHandler());
    return t;
  }
}

public class CaptureUncaughtException {
  public static void main(String[] args) {
    ExecutorService exec = Executors.newSingleThreadExecutor(
      new HandlerThreadFactory());
    exec.execute(new ExceptionThread2());
  }
} /* Output: (90% match)
HandlerThreadFactory@de6ced creating new Thread
created Thread[Thread-0,5,main]
eh = MyUncaughtExceptionHandler@1fb8ee3
run() by Thread[Thread-0,5,main]
eh = MyUncaughtExceptionHandler@1fb8ee3
caught java.lang.RuntimeException
*///:~

应该是创建一个线程的，但是我执行后却创建了两个线程，执行结果如下，请问是为什么？
concurrency.HandlerThreadFactory@7852e922 creating new Thread
created Thread[Thread-0,5,main]
eh = concurrency.MyUncaughtExceptionHandler@4e25154f
run() by Thread[Thread-0,5,main]
eh = concurrency.MyUncaughtExceptionHandler@4e25154f
concurrency.HandlerThreadFactory@7852e922 creating new Thread
created Thread[Thread-1,5,main]
eh = concurrency.MyUncaughtExceptionHandler@6a8a631a
caught java.lang.RuntimeException

Java线程创建方法......
答案就在这里：Java创建线程
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a threadfactroy 创建线程
Java编程思想中的样列代码：
package concurrency;

//: concurrency/CaptureUncaughtException.java
import java.util.concurrent.*;

class ExceptionThread2 implements Runnable {
public void run() {
Thread t = Thread.currentThread();
System.out.println("run() by " + t);
System.out.println(
"eh = " + t.getUncaughtExceptionHandler());
throw new RuntimeException();
}
}

class MyUncaughtExceptionHandler implements
Thread.UncaughtExceptionHandler {
public void uncaughtException(Thread t, Throwable e) {
System.out.println("caught " + e);
}
}