Java - How to throw RuntimeException

Question

I'm trying to throw an exception in my code like this:

throw RuntimeException(msg);

But when I build in NetBeans I get this error:

C:\....java:50: cannot find symbol
symbol  : method RuntimeException(java.lang.String)
location: class ...
        throw RuntimeException(msg);
1 error

Do I need to import something? Am I misspelling it? I'm sure I must be doing something dumb :-(

Answer 1

throw new RuntimeException(msg)

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

Answer 2

throw new RuntimeException(msg); // notice the "new" keyword

Answer 3

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.

Answer 4

You need to create the instance of the RuntimeException, using new the same way you would to create an instance of most other classes:

throw new RuntimeException(msg);

Answer 5

you will have to instantiate it before you throw it

throw new RuntimeException(arg0) 

PS: Intrestingly enough the Netbeans IDE should have already pointed out that compile time error

Answer 6

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.