JDBC FAQ part4

6:    How to establish a Database connection between java application and Database?

If we want to establish a connection between java application and the database we will the following piece of code.

Connection con= DriverMadoeer.getConnection(“jdbc:odbc:doe”,”doe”,”system”,”madoeer”);

Where getConnectin() is a static method from DriverMadoeer class, which can be used to return connection object.

7:  Basically Connection is an interface, how getConnection() will create an object for
      Connection interface?
Ans:   Connection is an interface from java.sql package, for which getConnection(_)  was return an anonymous inner class object of the Connection interface.

Note:-  Anonymous inner class is a nameless inner class, which can be sued to provide an implementation either for the interfaces or for abstract classes.

Eg:   interface I
         {
                void m1();
          }
         Class Outer
         {
                     I  i = new I(){
                                             public void m1()
                                             {
                                             
                                             }
                                             public void m2()
                                             {

}
                                           }
            }
            Outer o = new Outer();
            o.i.m1();   à  correct
            o.i.m2();   à  wrong

                        getConnection(_) is a static method from DriverMadoeer class, which will call internally  connect() method, this connect() will establish a virtual socket connection in between the java application and the database.
8:   What is the requirement to use Statement object?

• After establishing a connection between java application and the database we need to write the sql queries and we need to execute them.
• To execute the sql queries we will use some pre-defined library, which was defined in the form of Statement object,  PreparedStattement object and CallableStatement object.
• As per the application requirements we need to create either Statement object or CallableStatement object and PreparedStatement object.
• To create Statement object dwe will use the following method from connection object.

public  Statement createStatement()
Eg:     Statement st = con.createStatement();
9:  How to  execute SQL Queries from a java application?

To execute the sql queries we will use the following methods from Statement object.

• st.executeQuery(…)
• st.executeUpdate(…)
• st.execute(…)