为什么会陷入僵局

清单8.1中的代码“实践中的Java并发”

为什么代码死锁?是因为 rpt.call 在里面 main() 与执行器中的线程基本相同吗?

即使我用10个线程 exec = Executors.newFixedThreadPool(10); 还是僵局?

public class ThreadDeadlock {
  ExecutorService exec = Executors.newSingleThreadExecutor();

  public class RenderPageTask implements Callable<String> {
    public String call() throws Exception {
        Future<String> header, footer;
        header = exec.submit(new LoadFileTask("header.html"));
        footer = exec.submit(new LoadFileTask("footer.html"));
        String page = renderBody();
        // Will deadlock -- task waiting for result of subtask
        return header.get() + page + footer.get();
    }
  }

   public static void main(String [] args ) throws Exception {

        ThreadDeadlock td = new ThreadDeadlock();
        ThreadDeadlock.RenderPageTask rpt = td.new RenderPageTask();
        rpt.call();
    }
}