I have a method like this:
public void getSomething(){
...
}
I want to throw an Exception
inside getSomething()
. The compiler will not allow me to do that because my method doesn't allow Exception
to be thrown in there. But I need to throw a subclass of Exception
for my testing (I can't throw Unchecked Exception
). This is clearly a hack but I need it for my testing. I tried EasyMock but it doesn't allow me to do that either. Any ideas how to do that?
Thanks, Sean Nguyen
Method 1:
This post by Alexey Ragozin describes how to use a generics trick to throw an undeclared checked exception. From that post:
The trick relies on
throwUnchecked
"lying" to the compiler that the typeE
isRuntimeException
with its call tothrowAny
. SincethrowAny
is declared asthrows E
, the compiler thinks that particular call can just throwRuntimeException
. Of course, the trick is made possible bythrowAny
arbitrarily declaringE
and blindly casting to it, allowing the caller to decide what its argument is cast to - terrible design when coding sanely. At runtime,E
is erased and has no meaning.As you noted, doing such a thing is a huge hack and you should document its use very well.
Method 2:
You can also use
sun.misc.Unsafe
to this end. First you must implement a method that uses reflection to return that class's instance:This is necessary as calling
Unsafe.getUnsafe()
will typically throw aSecurityException
. Once you have the instance ofUnsafe
you can put its terrifying capabilities to use:Credit goes to this answer on the post https://stackoverflow.com/questions/5574241/interesting-uses-of-sun-misc-unsafe. I thought I'd mention this for completeness but it's probably better just to use the trick above instead of allowing
Unsafe
into your code.Method 3:
In the comments of the linked answer about using
Unsafe
, @bestsss points out a much simpler trick using the deprecated methodThread.stop(Throwable)
:In this case you would use
@SuppressWarnings("deprecation")
and once again document very fiercely. Again, I prefer the first trick for its (relative) cleanliness.I don't know what you were trying to do. You could just throw an unchecked exception inside your method and then test using JUnit like in my example below.
JUnit 4 test example:
Java has two kinds of exceptions, checked and unchecked. You must declare checked exceptions, but you don't have to declare unchecked exceptions.
RuntimeException
is the basic unchecked exception, so you can throw that without declaring it.As a side note, you probably don't want to throw a raw RuntimeException, but subclass it to something more specific to your needs. Any subclass of RuntimeException will be unchecked as well.