Software Interfaces in Practice
A piece of software provides access to computer resources (such as memory, CPU, storage, etc.) by its underlying computer system; the availability of these resources to other software can have major ramifications—sometimes disastrous ones—for its functionality and stability. A key principle of design is to prohibit access to all resources by default, allowing access only through well-defined entry points, i.e. interfaces.
The types of access that interfaces provide between software components can include: constants, data types, types of procedures, exception specifications and method signatures. In some instances, it may be useful to define public variables as part of the interface. It often also specifies the functionality of those procedures and methods, either by comments or (in some experimental languages) by formal logical assertions and preconditions.
The interface of a software module A is deliberately kept separate from the implementation of that module. The latter contains the actual code of the procedures and methods described in the interface, as well as other "private" variables, procedures, etc.. Any other software module B (that can be referred to as a client to A) that interacts with A is forced to do so only through the interface. One practical advantage of this arrangement is that replacing the implementation of A by another one that meets the same specifications of the interface should not cause B to fail—as long as its use of A complies with the specifications of the interface. (See also Liskov substitution principle.)
Read more about this topic: Software Interface, Software Interfaces
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