Lo que quiero hacer es crear una base de datos cerrarla luego abrirla y hacer una consulta. Las demas clases (player,team..) contienen atributos y metodos get y set.


Este es el codigo en java:

import com.db4o.*;
import com.db4o.query.*;
 
import java.io.File;
 
 
import java.util.Iterator;
 
public class Db4oTest {
    private static String filename;
 
 
    public Db4oTest() {
        filename = "c:/teamsdemo.yap";
    }
 
    public static void main(String[] args){
        Db4oTest tester = new Db4oTest();
        tester.createTestData();
        tester.queryByExampleDemo();
 
    }
 
    /**
     * creates test objects and stores them in new database file
     */
 
	private void createTestData(){
        System.out.println("Creamos base de datos");
 
        // Create Players
        Player p1 = new Player("Barry Bonds", 25, 0.362f);
        Player p2 = new Player("Marquis Grissom", 9, 0.279f);
        Player p3 = new Player("Ray Durham", 5, 0.282f);
        Player p4 = new Player("Adrian Beltre", 29, 0.334f);
        Player p5 = new Player("Cesar Izturis", 3, 0.288f);
        Player p6 = new Player("Shawn Green", 15, 0.266f);
 
        // Create Pitchers
        Player p7 = new Pitcher("Kirk Rueter",46, 0.131f, 9);
        Player p8 = new Pitcher("Kazuhisa Ishii",17, 0.127f, 13);
 
        // Create Teams
        Team t1 = new Team("Giants", "San Francisco", 91, 71);
        Team t2 = new Team("Dodgers", "Los Angeles", 93, 69);
 
        // Add Players to Teams
        t1.addPlayer(p1); p1.setTeam(t1);
        t1.addPlayer(p2); p2.setTeam(t1);
        t1.addPlayer(p3); p3.setTeam(t1);
        t2.addPlayer(p4); p4.setTeam(t2);
        t2.addPlayer(p5); p5.setTeam(t2);
        t2.addPlayer(p6); p6.setTeam(t2);
 
        // Add Pitchers to Teams
        t1.addPlayer(p7); p7.setTeam(t1);
        t2.addPlayer(p8); p8.setTeam(t2);
 
        // Open a new database
        new File(filename).delete();
        ObjectContainer db = Db4o.openFile(filename);
 
        // Store Teams - also stores associated Players
        //db.set(t1);
        db.store(t1);
        System.out.println("Stored " + t1);
        //db.set(t2);
        db.store(t2);
        System.out.println("Stored " + t2);
 
        // Close database
       db.close();
 
	}
 
 
 
    /**
     * Demonstrates query-by-example
     */
 
	private void queryByExampleDemo(){
 
 
        // Open database
        ObjectContainer db = Db4o.openFile(filename);
        // Retrieve a Player by creating an example Player object
        Player examplePlayer = new Player("Barry Bonds",0,0f);
        ObjectSet result=db.queryByExample(examplePlayer);
 
        System.out.println(result.size());
        while(result.hasNext()) {
            System.out.println(result.next());
        }
        result.reset();
 
        // Retrieve a Team and all Players
        Team exampleTeam = new Team("Dodgers",null, 0, 0);
        result=db.queryByExample(exampleTeam);
 
        // List results
        System.out.println(result.size());
        while (result.hasNext()){
            Team t = (Team) result.next();
            System.out.println(t);
            Iterator itr = t.getPlayers().iterator();
            while (itr.hasNext()) {
                Player p = (Player) itr.next();
                System.out.println(p);
            }
        }
 
        // Close database
        db.close();
    }

   
   Salta el siguiente error:

Exception in thread "main" java.lang.ClassCastException: Player cannot be cast to com.db4o.reflect.generic.GenericObject
   at com.db4o.reflect.generic.GenericField.get(GenericField.java:36)
   at com.db4o.internal.FieldMetadata.getOn(FieldMetadata.java:582)
   at com.db4o.internal.FieldMetadata.collectConstraints(FieldMetadata.java:338)
   at com.db4o.internal.ClassMetadata$3.apply(ClassMetadata.java:447)
   at com.db4o.internal.ClassMetadata.forEachDeclaredAspect(ClassMetadata.java:1968)
   at com.db4o.internal.ClassMetadata.forEachAspect(ClassMetadata.java:1949)
   at com.db4o.internal.ClassMetadata.forEachField(ClassMetadata.java:1939)
   at com.db4o.internal.ClassMetadata.collectConstraints(ClassMetadata.java:443)
   at com.db4o.internal.query.processor.QConObject.associateYapClass(QConObject.java:82)
   at com.db4o.internal.query.processor.QConObject.byExample(QConObject.java:421)
   at com.db4o.internal.PartialObjectContainer.queryByExampleInternal(PartialObjectContainer.java:757)
   at com.db4o.internal.PartialObjectContainer.queryByExample(PartialObjectContainer.java:741)
   at com.db4o.internal.ExternalObjectContainer.queryByExample(ExternalObjectContainer.java:75)
   at com.db4o.internal.ExternalObjectContainer.get(ExternalObjectContainer.java:71)
   at Db4oTest.queryByExampleDemo(Db4oTest.java:102)
   at Db4oTest.main(Db4oTest.java:25)