它们都实现了Throwable接口
catch Exception 是捕捉不到Error的
而且，JAVA还要求我们不要捕捉Error：
An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions. The ThreadDeath error, though a "normal" condition, is also a subclass of Error because most applications should not try to catch it.