DLL

dynamic link library (DLL)

package the class in DLL, then this class can be reused

when the implementation of class is modified, the client program does not need to rebuild

problem:

ex:

test.DLL has two version,

version 1: class Test is 4 bytes

version 2: class Test is 8 bytes

If user installed test.DLL version 2, then client program originally use test.DLL version one will fail because it thinks the class Test is 4 bytes