How to throw RuntimeException ("cannot find symbol")

throw new RuntimeException(msg);

You need the new in there. It's creating an instance and throwing it, not calling a method.

An Exception is an Object like any other in Java. You need to use the new keyword to create a new Exception before you can throw it.

throw new RuntimeException();

Optionally you could also do the following:

RuntimeException e = new RuntimeException();throw e;

Both code snippets are equivalent.

Link to the tutorials for completeness.

As everyone else has said, instantiate the object before throwing it.

Just wanted to add one bit; it's incredibly uncommon to throw a RuntimeException. It would be normal for code in the API to throw a subclass of this, but normally, application code would throw Exception, or something that extends Exception but not RuntimeException.

And in retrospect, I missed adding the reason why you use Exception instead of RuntimeException; @Jay, in the comment below, added in the useful bit. RuntimeException isn't a checked exception;

• The method signature doesn't have to declare that a RuntimeException may be thrown.
• Callers of that method aren't required to catch the exception, or acknowlege it in any way.
• Developers who try to later use your code won't anticipate this problem unless they look carefully, and it will increase the maintenance burden of the code.