+e 与 e 在 throw Exception 中的区别

Question

In Java, what is the difference between following 2 statements:

throw new Exception ("msg" + e);

and

throw new Exception ("msg", e);

I know both of them are possible. Is there any difference in how they work behind the scenes and which is a better practice to use?

Answer 1

The first one creates a new exception with a message that is a string concatenation of msg and the string representation of e . For this the toString method of e will be used. This effectively gives the message of the original exception and concatenates it with the string msg .

The second one creates a new exception with only the message msg and adds the original exception as a cause. Hence, more information from the original exception is available, for example the stack trace.

Answer 2

throw new Exception ("msg" + e); throws a new Exception with a message that's a concatenation of "msg" and e.toString() , losing e stacktrace in the process.

throw new Exception ("msg", e); throws a new Exception with a message "msg" and e as the cause.

Answer 3

throw new Exception ("msg" + e); throws a new Exception with a message that's a concatenation of "msg" and e.toString() , losing e stacktrace in the process.

throw new Exception ("msg", e); throws a new Exception with a message "msg" and e as the cause.