ResultSet is a interface
More gnerally,ResultSet is a class involves a table returned by executeQuery cluase from jdbc，which includes the whole information we wanna get from our query，however if we want to retrive these info in java applet ，jdbc provides us a cursor.Let's see how Java API explain it
After reading this explanation , we can understand the meaning of whlie (rs.next()) {...}
In the while loop,we use cursor to access each row，but here comes the problem：how could we convert the underlying data in the set pointed by cursor to Java type?Here are the explanation from Java API：
We must provide a parameter to getter methods we invoke,which stands for the column that we wanna get information from.As for the parameter,API also give us some details about it.Let's take a look at it:
The last thing I think that our attention should be paid to is that the lifecycle of the ResultSet
