是否被应用到不具有的try-catch错误抛出一个异常的函数在JVM优化？

Question

There is a question What is the difference between try-catch and throws Exception in terms of performance? .

A follow-up question is "Does the JVM optimization being applied to a function that doesn't have try-catch bug throws a exception?". For example, all methods throw their exceptions and the main method has a try-catch to surround all methods and codes. In this case, according to "Effective Java":

Placing code inside a try-catch block inhibits certain optimizations that modern JVM implementations might otherwise perform.

JVM won't do some optimization for the code in the main method. The question is: dose the JVM optimize the code in those methods who throw exceptions?

Answer 1

If you mean the throws clause, then definitely not. Note that all methods sort of have an "invisible throws RuntimeException, Error clause", ie, they may throw something.

Note also, that there's nothing like checked exceptions on the JVM level, it's a pure Java source feature which doesn't exist in the bytecode (and there are many other languages running on the JVM and having no checked exceptions; AFAIK Java is the only experiment).

Actually throwing exceptions is expensive, but basically any method can throw some. Even an empty method can in theory throw a StackOverflowError . It only gets expensive, when an exception actually happens.

For a try-catch block, there's just an entry somewhere which gets consulted, when an exception gets actually thrown, otherwise it doesn't get used. It may prevent some optimizations, which would make it impossible to use this information, or not; the JVM gets better and better.

Anyway, adding a throws clause has no performance impact and it's the right thing most of the time.