Coming back to the above post by Anton, yes, the kind of runtime type checking exists in lots of popular Java frameworks, even today. And this is where frameworks like Guice and EasyMock really shine with their strongly typed API sets that make you feel more secure within the confines of your IDE and refactoring abilities. The Morale When you are programming in a statically typed language, use appropriate language features to make most of your type checking at compile time. This way, before you hit the run button, you can be assured that your code is well-formed within the bounds of the type system. And you have the power of easier refactoring and cleaner evolution of your codebase.