Data structure Set and List in java

Normally when we create a bean, we define it by an interface with the bean being a concrete implementation of it. This provides the benefit of being able to swap out implementations just by changing the configuration file (assuming the other implementations were already created). If the bean was defined by an implementation instead of an interface, when you decide you want to switch out one implementation for another, you will need to find all of its uses (which could exist in a lot of separate files).