java - 调试器中的 java 下载管理器

Question

有时在调试过程中会出现 sun.jkernel.DownloadManager。为什么会这样？

http://www.docjar.com/html/api/sun/jkernel/DownloadManager.java.html

/**
 * Handles the downloading of additional JRE components.  The bootstrap class
 * loader automatically invokes DownloadManager when it comes across a resource
 * that can't be located.
 *
 *@author Ethan Nicholas
 */
 public class DownloadManager extends BootClassLoaderHook {