In JMockIt, what is a @Mock final parameter

Question

I'm completely new to JMockIt. In the tutorial I see example codes that uses the final modifier for a @Mocked parameter e.g.

  @Test
   public void doSomethingHandlesSomeCheckedException(@Mocked final DependencyAbc abc) throws Exception
   {
    ...
   }

What does final mocked parameter mean here? Sometimes, "final" is not used. What is the difference?

Answer 1

This is merely a Java language issue, nothing to do with JMockit itself. For a method parameter or local variable to be used inside an inner class (anonymous or not), the Java compiler requires it to be declared as final.

Answer 2

From the JMockit tutorial:

"For a mock parameter declared in a test method, an instance of the declared type will be automatically created by JMockit and passed by the JUnit/TestNG test runner when calling the test method. Therefore, the parameter value will never be null.

For a mock field, an instance of the declared type will be automatically created by JMockit and assigned to the field, unless it's a final field. In such case, a value should be created and assigned to the field explicitly in test code. This value can be null, though, which is perfectly valid for a mocked class if only constructors and static methods are going to be called on it."

http://jmockit.googlecode.com/svn/trunk/www/tutorial/BehaviorBasedTesting.html#declaration

Keep in mind that a mock parameter/field is any annotated with @Mocked or @Injectable.