Can not use executeQuery()

Question

I'm making an application to get data from Database , But I can't use executeQuery in my code. This is exception of my code : java.lang.ClassCastException: org.apache.derby.client.am.ClientStatement cannot be cast to java.beans.Statement at Database.main(Database.java:28) Where is the problem?

Connection MyconObj=null;
Statement MystateObj =null;
ResultSet MyresObj = null;
try {
 MyconObj = DriverManager.getConnection("jdbc:derby://localhost:1527/students", "root", "root");
 MystateObj = (Statement) MyconObj.createStatement();
 String query = "SELECT * FROM ROOT.INFORMATION";
 ResultSet MyresObj = MystateObj.executeQuery(query);
 while(MyresObj.next()){
 int id = MyresObj.getInt("id");
 String name = MyresObj.getString("name");
 String lastname = MyresObj.getString("lastname");
 System.out.println(id + "" + name + "" + lastname);
 }
} catch (Exception e) {
 e.printStackTrace();
}

• FindOutIslamNow: what is the exception message?
• Rann Lifshitz: What do you mean by 'can't use executeQuery in my code.' ? Are you getting an exception at runtime?
• Mark Rotteveel: Please provide more information, like the error or exception stacktrace. And I strongly suggest that you start using the Java naming conventions (variables and fields starting with a lowercase letter: that makes your code more readable for people familiar with those conventions (ie most Java developers).
• Mohammad Goudarzi: @FindOutIslamNow java.lang.ClassCastException: org.apache.derby.client.am.ClientStatement cannot be cast to java.beans.Statement at Database.main(Database.java:28)
• Mark Rotteveel: Remove the cast and make sure that you import java.sql.Statement, not java.beans.Statement.

Answer 1

This is a classic example of how classes with the same name can cause confusion and runtime exceptions:

MystateObj = (Statement) MyconObj.createStatement();

The imports used by the implementation have not been included in the OP code, however, based on the thrown exception:

java.lang.ClassCastException: org.apache.derby.client.am.ClientStatement cannot be cast to java.beans.Statement

The Statement class used in the cast is java.beans.Statement, which has probably been imported. The object which has been returned by MyconObj.createStatement() is of the type org.apache.derby.client.am.ClientStatement and this causes the casting exception during runtime - the returned Object is an extension of java.sql.Statement, as mentioned in the comments above (by Mark Rotteveel).

The import of the Statement is correct but from the wrong library. This can easily occur when using IDEs which allow auto import generation (when more then one class matches the used class name, a drop-down list is displayed for possible imports. Selecting the wrong import is a common event, unfortunately).