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Notice that if an object is in a class that implements an interface then the compiler can make sure that all the operations applied to the object are in the interface. The actual class of the object does not matter.... all that matters is that the object's class fits the interface. This is like a modular phone jack!
There are many ways to implement the same interface. Each implementation completes the function/operation/subprogram definitions in a special way.
An abstraction has some details hidden (to-be-announced) and some defined.
An abstract subprogram, function, or operation has no body. An abstract class has a mixture of defined functions, abstract functions, and variables.
There are many ways to implement (completely define) an abstraction. The defined parts provide a framework. The undefined parts are places to plug in specific pieces of code into the framework. An example would be a class that defines a 'sort' function but does not define a function that tests if two objects are in order. By supplying the definition of this function you can plug-in your own sort order.
A concrete module has all its details defined. There is enough information available for objects of a concrete class to be constructed. As a result you can do any of the defined operations with objects that have a concrete type.
A dotted or dashed open arrow joins an implementation to its abstractions. A closed dotted arrow shows that a class uses an interface to access an implementation. There is a special "lollipop" notation indicating a piece of code that implements an interface. Or you can add <<interface>> as a stereotype to a class box.
In UML 2.0 the arrow and lollipop notation has become a "cup-and-ball" notation.
Here is an example, in Java we may want to create a class that is an Applet in a web page, and also reacts to what the user does with mouse, and is also multithreaded. The diagram shows the Java Virtual Machine using our class via two interfaces:
Client programmer: I don't worry about how you code it as long as
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