Go to the source! Grady Booch says (in Object Oriented Analysis and Design, page 49, second edition):
Abstraction and encapsulation are complementary concepts: abstraction
focuses on the observable behavior of an object… encapsulation
focuses upon the implementation that gives rise to this behavior…
encapsulation is most often achieved through information hiding, which
is the process of hiding all of the secrets of object that do not
contribute to its essential characteristics.
In other words: abstraction = the object externally; encapsulation (achieved through information hiding) = the object internally,
Example:
In the .NET Framework, the System.Text.StringBuilder class provides an abstraction over a string buffer. This buffer abstraction lets you work with the buffer without regard for its implementation. Thus, you’re able to append strings to the buffer without regard for how the StringBuilder internally keeps track of things such the pointer to the buffer and managing memory when the buffer gets full (which it does with encapsulation via information hiding).
rp