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Java Forum / General / April 2008Why can't we "new" a Statement object?
Why do we have to use the Connection object to produce a Statement object? Similar question like, Why do we have to use the DriverManager to produce a Connection object? Can't we create a Connection object via Connection myConn=new Connection()? > Why do we have to use the Connection object to produce a Statement > object? Similar question like, Why do we have to use the DriverManager > to produce a Connection object? Can't we create a Connection object > via Connection myConn=new Connection()? The pattern is called "Factory" Connection may not be a concrete type. It might not even be a class! You don't know what type of Connection you're going to get unless you know what Driver you're using. etc... Same goes with Statement. Different drivers may create different Connections, which create different Statements, but all *you* know about are the static abstract base classes/interfaces.  SignatureDaniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> tenxian wrote: >> Why do we have to use the Connection object to produce a Statement >> object? Similar question like, Why do we have to use the DriverManager >> to produce a Connection object? Can't we create a Connection object >> via Connection myConn=new Connection()? > The pattern is called "Factory" > Connection may not be a concrete type. It might not even be a class! Indeed, Connection certainly is not a concrete type: <http://java.sun.com/javase/6/docs/api/java/sql/Connection.html> The whole point of programming to interfaces is to prevent you from instantiating a class like Connection cxn = new VendorSpecificConnection(); The problem is that this code is now locked in permanently to this particular connection class. With DriverManager.getConnection(), the client code has no clue what the actual class is. That means it can run without recompilation or redeployment on any class. By preventing the client from even seeing what concrete classes are available, the API makes it much easier to write stable, robust, efficient, portable code. Under JPA one uses injection via annotations, and life gets sweeter still. In theory. SignatureLew On Apr 29, 8:24 am, Daniel Pitts <newsgroup.spamfil...@virtualinfinity.net> wrote: > > Why do we have to use the Connection object to produce a Statement > > object? Similar question like, Why do we have to use the DriverManager [quoted text clipped - 13 lines] > -- > Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> What is a Factory in Java? > On Apr 29, 8:24 am, Daniel Pitts > <newsgroup.spamfil...@virtualinfinity.net> wrote: [quoted text clipped - 13 lines] > > What is a Factory in Java? Same as in other languages. See http://en.wikipedia.org/wiki/Factory_method_pattern ! Arne > On Apr 29, 8:24 am, Daniel Pitts > <newsgroup.spamfil...@virtualinfinity.net> wrote: [quoted text clipped - 4 lines] >> >> The pattern is called "Factory" > What is a Factory in Java? http://en.wikipedia.org/wiki/Factory_method_pattern You can look these things up yourself, you know. Matt Humphrey http://www.iviz.com/ On Mon, 28 Apr 2008 18:29:19 -0700 (PDT), tenxian <hi.steven.tu@gmail.com> wrote, quoted or indirectly quoted someone who said : >What is a Factory in Java? see http://mindprod.com/jgloss/factorymethod.html It is a design pattern for constructing objects. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > Why do we have to use the Connection object to produce a Statement > object? Similar question like, Why do we have to use the DriverManager > to produce a Connection object? Can't we create a Connection object > via Connection myConn=new Connection()? You can: Connection myConn = new FoobarDatabaseSpecificConnection(); but you will hopefully never be able to get that type of code through code review, because the code is Foobar database specific. It is a core concept in Java that database code should be database independent. DriverManager.getConnection enables you to use the same code for different databases (the connection URL can be put in a configuration file). Arne On Mon, 28 Apr 2008 17:10:52 -0700 (PDT), tenxian <hi.steven.tu@gmail.com> wrote, quoted or indirectly quoted someone who said : >Why do we have to use the Connection object to produce a Statement >object? Similar question like, Why do we have to use the DriverManager >to produce a Connection object? Can't we create a Connection object >via Connection myConn=new Connection()? This derives from the fact that every SQL database may implement things quite differently. All that gets nailed down is the INTERFACE, not the classes or even an abstract class basic implementation. The code you run for Statement.someMethod is completely different for Oracle vs MySQL . New presumes a common class and common implementation. When you don't have that you need a pluggable mechanism and a factory to get you the objects you need. That's one thing the driver does. You will see the same sort of thing in JCE where you can have different implementors. JavaMail allows different implementations so it too likely works this way though it has been a while since I fiddled with those details. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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