`A` RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.
`B` A method is not required to declare in its throws clause any subclasses of RuntimeExeption that might be thrown during the execution of the method but not caught
`C` An RuntimeException is a subclass of Throwable that indicates serious problems that a` reasonable application should not try to catch.
`D` NullPointerException is one kind of RuntimeException
四个选项都来自于Java API原文.
A选项是RuntimeException的定义;
B选项是把Error的第二段定义拿来改掉换成RuntimeException,但这样说对于RuntimeException也没错;
C选项也是把Error的定义换成了RuntimeException,但这里的"indicates serious problems"不应该用在RuntimeException上,Error才表示严重的错误,RuntimeException并不是.
D选项显然.
具体可查看API,网址http://docs.oracle.com/javase/7/docs/api/java/lang/Error.html
