programming-for-dummies

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Sharing Code with Inheritance
Protecting code from other programmers
Objects isolate data from other parts of the program, but objects can also
isolate subprograms from other programmers.
Without objects, someone might write a useful subprogram that everyone
else working on the program can use. One programmer might find that subprogram
perfect whereas a second programmer might find that subprogram
doesn’t quite do what he wants it to do, so he goes into the subprogram and
changes the code.
These changes wreck the subprogram for the first programmer, who now has
to go back and fix the changes made by the second programmer. These
changes make the subprogram work good for the first programmer, but now
wreck the subprogram for the second programmer, and so on in an endless
cycle.
The problem is that the more people you have working on the same program,
the more likely someone might accidentally modify one part of a
program without notifying the other programmers. Even one change in a program
can affect another part of that same program, so object-oriented programming
defines distinct boundaries that keep programmers from
modifying code stored in objects created by someone else.
When creating an object-oriented program, every programmer is given control
of certain objects and no one is supposed to modify the code in any
objects but his own.
Objects let you physically store the source code for your entire object in a
separate file, called a class file or just a class. At this point, a class is no different
than storing a group of related subprograms in a separate file and
keeping other programmers from modifying that separate file. However, the
difference becomes more apparent when you want to reuse code.
Encapsulation serves two purposes:
✦ Protects data from being changed by other parts of a program
✦ Protects subprograms from being changed by other programmers
Sharing Code with Inheritance
After programmers write some useful subprograms, they often store those
subprograms in separate files for other programmers to use. However, no
one is supposed to modify these subprograms.