The abbreviation impl is used in a lot of libraries; What does it mean?

Question

I've seen impl used as namespaces and as a class suffix in a number of different .net and Java libraries. I just want to know what it means and why it is used.

Answer 1

It's short for "implementation". Generally it's used when the parent package contains abstract classes, interfaces, and perhaps some factory classes which are the main point of access, and then the impl package contains various concrete implementations of those abstract classes and interfaces.

Answer 2

It stands for Implementation.

It's a Java convention.

Often in java (particularly J2EE) you will get an object from some factory, and then use it.

That object's type is often given to you as an interface, so that you don't need to know the actual class, just its methods.

An impl class is usually a class that implements the behaviour described by one of these interfaces.