Re: DriverManager in JDBC
asit wrote:
In java [sic], we can't instantiate DriverManager class becoz [sic] the
constructor is private.
Why this is so ??? [sic]
Why the constructor is provided ??? [sic]
You only need one question mark at the end of a sentence to indicate
an interrogative in English.
See Joshua Bloch's excellent book /Effective Java/, Item 1, "Consider
static factory methods instead of constructors" for a detailed
explanation of this idiom.
The short version is that 'java.sql.DriverManager' is a class that you
should never instantiate. It is a utility class that has no state of
its own and all its methods are static (class level). It makes no
sense ever to have an instance of the class, so the API designer
ensured that no client can instantiate the class.
It also prevents specious inheritance of the class. ("Design and
document for inheritance or else prohibit it", /ibid./) It makes as
little sense to inherit from a class of nothing but static methods as
it does to instantiate it.
Some of the methods in 'java.sql.DriverManager' are factory methods
that return implementation instances by their interface type. By
keeping the actual concrete type hidden, the factory has the
flexibility to provide any implementing type, even a different one
from time to time, without damage to client code. This is part of
what is sometimes called, "programming to the interface" or
"programming to the type", a best practice of defining behaviors at
the interface level and generally hiding the concrete classes
involved.
--
Lew