java.sql.SQLException: No suitable driver

Hi,
I m developing a application in which  i need to connect to postgres Database lying on remote host.
when I tried to connect to remote database Using following code:

connection=DriverManager.getConnection("jdbc:postgresql://"+host+":"+port+"/sms",user,pwd);

 I got error like this:

java.sql.SQLException: No suitable driver

what could be the cause? What could be the solution???

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