Thread: how to resolve awt-eventqueue-0 java.lang.nullpointerexception

during the execution of the my application java (developed following design pattern as front controller, dao factory, business object, singleton) i have a problem of connection at this line : Statement st = connessione.createStatement(ResultSet.TYPE_SCROLL_ INSENSITIVE, ResultSet.CONCUR_READ_ONLY); I using the rdbms mysql this problem is presented when I do much query on my db. This is my class that handle the connection with my database.

public class SQLDAOFactory extends DAOFactory implements AgroludosDAO {
 
private static final String dbPath="jdbc:mysql://localhost/agroludos";
private static final String dbUser="root";
private static final String dbPass="root";
 
private SQLDAOFactory SQLFactory;
public static Connection connectDB() {
    Connection connessione = null;
 
    // Caricamento del driver
    try {
        System.out.println("Caricamento Database. Attendere...");       
        connessione = DriverManager.getConnection(dbPath, dbUser, dbPass);
        System.out.println("Connessione OK");
    } catch (SQLException e) {
        JPane.setError(JPane.WARNING_CONNECTION_DATABASE);
        JPane.getError();
       }
 
    return connessione;
}

and this is a code that realize my query:

try {
 
        //Crea uno statement per l'interrogazione del database
        Statement st = connessione.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
 
        //Trace
        System.out.println("Database -> Interrogazione SQL: " + query);     
 
        //Crea un ResultSet eseguendo l'interrogazione desiderata
        ResultSet tabellina = st.executeQuery(query);
        //Trace
        System.out.println("query ok"); 
        return new TableModelCustom(tabellina);
 
    } catch (SQLException e) {
        e.printStackTrace();
        return null;
    }
 
}

How to resolve this problem? it is urgent!

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this problem is presented when I do much query on my db

What problem is presented? If you're getting an error message, please post that entire message.

Originally Posted by GregBrannon

Thread moved.

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What problem is presented? If you're getting an error message, please post that entire message.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at agroludos.database.TipoCompetizioneSQL.getDati(Tip oCompetizioneSQL.java:58)
at agroludos.database.SQLDAOFactory.getDati(SQLDAOFac tory.java:348)
at agroludos.business.BOController.getBO(BOController .java:329)
at agroludos.business.BOController.selectedRow(BOCont roller.java:238)
at agroludos.boundary.EditorManagerCompetizione$4.mou sePressed(EditorManagerCompetizione.java:312)
at java.awt.AWTEventMulticaster.mousePressed(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent( Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(U nknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unkno wn Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

this is code TipoCompetizioneSQL.getDati and the error is at line :
Statement enunciato = connessione.createStatement(ResultSet.TYPE_SCROLL_ INSENSITIVE, ResultSet.CONCUR_READ_ONLY);

public static ArrayList<String> getDati(int id_row){
 
		int id = 0;
		String tipo = "";
		String query = "select id,tipo from tipi_competizione where id = "+id_row+";";
		try{
			connessione = SQLDAOFactory.connectDB();
			Statement enunciato = connessione.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
			ResultSet risultato = enunciato.executeQuery(query);
 
 
			while (risultato.next()) {
				id = risultato.getInt("id");
				tipo = risultato.getString("tipo");
			}			
		} catch (SQLException e) {
			JPane.setError(JPane.WARNING_CONNECTION_DATABASE);
			JPane.getError();
		}
		// Popolamento dell'ArrayList con i dati estratti dal database
		ArrayList<String> campi = new ArrayList<String>();
 
		String id_str = Integer.toString(id);
		campi.add(id_str);
		campi.add(tipo);
		return campi;	
	}

A Null Pointer Exception, or NPE, indicates that you've attempted to access an object that has not been initialized or was initialized to null. An object in the line pointed to by the error is null and needs to be initialized to something other than null. You can find which is the offending object by code inspection or adding print statements to print each object.

Originally Posted by GregBrannon

A Null Pointer Exception, or NPE, indicates that you've attempted to access an object that has not been initialized or was initialized to null. An object in the line pointed to by the error is null and needs to be initialized to something other than null. You can find which is the offending object by code inspection or adding print statements to print each object.

I have understood that the problem is an object that is null, but this problem don't presented it only in TipoCompetizioneSQL but also in other class and all at same line:
Statement enunciato = connessione.createStatement(ResultSet.TYPE_SCROLL_ INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
Then the problem I think that is the connection that is null, but this is strange because before this error I did others query without problem.

Then the problem I think . . .

What you suspect can be easily verified. Once verified (or not) work backwards to determine why something changed and correct it so that the change does not occur.

Originally Posted by GregBrannon

What you suspect can be easily verified. Once verified (or not) work backwards to determine why something changed and correct it so that the change does not occur.

the problem is connection because in consolle don't have Connessione OK that comes System.out.println("Connessione OK");.
What can I do to solve this problem? what are the changes that can be made?
it's urgent because it is a progam that I have to deliver monday!