About Connection, ResultSet, Statement interfaces....

Question

hi ,
Connection, ResultSet, Statement etc.. all are the interfaces. But when i am writing the codes like,
Statement stmt= con.createStatement();
ResultSet rs= stmt.excuteQuery("select * from student_mst");
where con is the instance of Connection interface.
Therefore my question is that since all those(Connection,ResultSet,Statement) are interfaces then how the methods createStatement(),excuteQuery(String sql) are being executed where as those methods are only the declarations in those interfaces,nothing else.

Answer 1

ok.......
So can u tell me in this case, actualy which class is
implenting the Statement interface such that
"executeQuery(String)" is working properly.....??????Hello,
First you need to understand interface and its working.. I will write one example code for u and I think this may hel how Connection, Statement and ResultSet work
This is out main Class
public class Main {
     public static void main(String[] args) {
          Connection con = DriverManager.getConnection();
          Statement stmt = con.createStatement();
          ResultSet rs = stmt.executeQuery("My Query");
          rs.getString();
}Connection.java
public interface Connection {
     public Statement createStatement();
}Statement.java
public interface Statement {
     ResultSet executeQuery(String sql);
}ResultSet.java
public interface ResultSet {
     public String getString();
}DriverManager.java
public class DriverManager {
     public static Connection getConnection()     {
          System.out.println("Calling getConnection()...");
          return new ConnectionImpl();
}Following are the implementstions of the interfaces
ConnectionImpl.java
public class ConnectionImpl implements Connection {
     public Statement createStatement() {
          System.out.println("Calling createStatement()...");
          return new StatementImpl();
}StatementImpl.java
public class StatementImpl implements Statement{
     public ResultSet executeQuery(String sql) {
          System.out.println("Calling executeQuery()...");
          return new ResultSetImpl();
}ResultSetImpl.java
public class ResultSetImpl implements ResultSet{
     public String getString() {
          System.out.println("Calling getString()...");
          return "My String";
}And the Output is
Calling getConnection()...
Calling createStatement()...
Calling executeQuery()...
Calling getString()...
I suppose now you can understand how the Connection, Statement and ResultSet interfaces work