Nullpointer & sql exception - Combobox databinding

[aborgeld]

Hi Guys,

I was figuring out how to get data in the combobox, that works, but now i get 2 exceptions and i hope you can help me to let me see where i go wrong.




View (Form) code:

private void setInitWaarden(){

    initComponents();
    
    codeComboBox.removeAllItems();
    students = Student.getAllStudenten();
    for (int teller=0;teller<students.length;teller++)
      System.out.println(students[teller].getCode());
    
    codeComboBox.addItem("");
    Student student;
      for (int teller=0;teller<students.length;teller++) {
      student = students[teller];
      System.out.println(student.getCode());
      codeComboBox.addItem(student.getCode());

     }

Methods in class Student

public static Student[] getAllStudenten() {
    return getStudentCode ("select * from student order by code");
  }

    private static Student[] getStudentCode(String query){

    ResultSet r = Database.executeSelectQuery(query);

    int aantalStudenten = Database.getAmountResultSet(r);
    Student[] studenten = new Student[aantalStudenten];

     try {
        r.next();
         for (int teller=0; teller < aantalStudenten; teller++) {
            Student value = new Student();
            value.code = r.getInt("code");
            value.setAchternaam(r.getString("achternaam"));
            //System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
            value.setBetaald(r.getInt("betaald"));

             studenten[teller] = value;
             r.next();
        }
      }

[aborgeld]

Error: he gets his results: like 3, 4, 5. But he has to start with 2:

See attachtment, database file (2 names are grade out due privacy).

init:
Deleting: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
deps-jar:
Updating property file: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
compile:
run:
Student: getAllStudenten: java.sql.SQLException: After end of result set
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
After end of result set
S1000
0
3
4
5
at view.OverzBetaalStudent.setInitWaarden(OverzBetaal Student.java:36)
at view.OverzBetaalStudent.<init>(OverzBetaalStudent. java:25)
at view.Hoofdscherm.studentPaylButtonActionPerformed( Hoofdscherm.java:177)
at view.Hoofdscherm.access$700(Hoofdscherm.java:14)
at view.Hoofdscherm$8.actionPerformed(Hoofdscherm.jav a:99)
at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed (AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed (DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultB uttonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.jav a:6267)
at javax.swing.JComponent.processMouseEvent(JComponen t.java:3267)
at java.awt.Component.processEvent(Component.java:603 2)
at java.awt.Container.processEvent(Container.java:204 1)
at java.awt.Component.dispatchEventImpl(Component.jav a:4630)
at java.awt.Container.dispatchEventImpl(Container.jav a:2099)
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.LightweightDispatcher.retargetMouseEvent( Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(C ontainer.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Conta iner.java:4168)
at java.awt.Container.dispatchEventImpl(Container.jav a:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478 )
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 599)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:122)
BUILD SUCCESSFUL (total time: 7 minutes 53 seconds)

[travishein]

try {
r.next();
for (int teller=0; teller < aantalStudenten; teller++) {
Student value = new Student();
value.code = r.getInt("code");
value.setAchternaam(r.getString("achternaam"));
//System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
value.setBetaald(r.getInt("betaald"));

studenten[teller] = value;
r.next();
}
}

instead of invoking the r.next() inside the for loop, also us it as a condition

 try {
        int teller  = 0;
        while (r.next() && teller < aantalStudenten) {
            Student value = new Student();
            value.code = r.getInt("code");
            value.setAchternaam(r.getString("achternaam"));
            //System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
            value.setBetaald(r.getInt("betaald"));

             studenten[teller] = value;
             teller++;
        }
      }

[aborgeld]

Thanks, one down, one to go. I understand the problem with the sql exception now. But how why do i get the null pointer exception with this code in the View(form)?

private void setInitWaarden(){

    initComponents();
    
    codeComboBox.removeAllItems();
    
    students = Student.getAllStudenten();
    for (int teller=0;teller<students.length;teller++)
        System.out.println(students[teller].getCode());
    
    codeComboBox.addItem("");
    Student student;
      for (int teller=0;teller<students.length;teller++) {
      student = students[teller];
      System.out.println(student.getCode());
      codeComboBox.addItem(student.getCode());

     }
    }

Exception:

init:
Deleting: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
deps-jar:
Updating property file: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
Compiling 1 source file to C:\Users\Andre\Documents\NetBeansProjects\academie \build\classes
compile:
run:
Student: getStudenten: betaald 1
Student: getStudenten: betaald 1
Student: getStudenten: betaald 0
3
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
4
5

[aborgeld]

These are the to String methods

 public String toString() {

    String output = "";
    output += getCode();
    output += getCode() + "  " + getAchternaam() + "  " ;
    output += getGeboortedatum() + "  " + getOpleiding() + "  ";
    output += slber.getAchternaam();
    return output;
  }

  public String toDescriptiveString() {
    return achternaam + " heeft " + (heeftBetaald ? "wel " : "niet ") + "betaald";
  }

[travishein]

what is the line number in this that generates the nill pointer exception?

my guess is somehow a student in the array of results is null, because the number of students returned from the Database.getAmountResultSet(r); is not giving the same number as we get from the while (r.next()) part. its possible the get amount is reading the values first.

maybe combine these,

    ResultSet r = Database.executeSelectQuery(query);

    List<Student> list = new ArrayList<Student>()

      try {
        while (r.next() && teller < aantalStudenten) {
            Student value = new Student();
            value.code = r.getInt("code");
            value.setAchternaam(r.getString("achternaam"));
            //System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
            value.setBetaald(r.getInt("betaald"));

             list.add(value);
             teller++;
        }
      }
      // if you need this list as an array and the total count, 
      int aantalStudenten = list.size();
      Student[] studenten = list.toArray(new Student[0]);

where I read results into a list and let it tell me how many there are, instead of calling that separate function anymore.

[aborgeld]

Hello Travishein,

Thanks for your help!

The exception comes in the view (form) in line 37

for (int teller=0;teller<students.length;teller++)
System.out.println(students[teller].getCode()); //exception start


I think your right i get another result


I got the arraylist method working in this way but with no results and then ofcourse no exception

private static Student[] getStudentCode(String query){

    ResultSet r = Database.executeSelectQuery(query);
    List aList = new ArrayList<Student>();
    
    int aantalStudenten = aList.size();
    Student[] studenten = (Student[]) aList.toArray(new Student[0]);
   
   
 try {
     
     
        int teller  = 0;
        while (r.next() && teller < aantalStudenten) {
            Student value = new Student();
            value.code = r.getInt("code");
            value.setAchternaam(r.getString("achternaam"));
            System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
            value.setBetaald(r.getInt("betaald"));

             aList.add(value);
             teller++;

        }
      }

     catch (SQLException e) {
      System.out.println("Student: getAllStudenten: " + e.toString());
      System.out.println(e.getMessage() + "\n" + e.getSQLState() + "\n" + e.getErrorCode());
    }


    return studenten;

  }

[aborgeld]

the whole exception:

init:
Deleting: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
deps-jar:
Updating property file: C:\Users\Andre\Documents\NetBeansProjects\academie \build\built-jar.properties
compile:
run:
3
4
5
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at view.OverzBetaalStudent.setInitWaarden(OverzBetaal Student.java:37)
at view.OverzBetaalStudent.<init>(OverzBetaalStudent. java:25)
at view.Hoofdscherm.studentPaylButtonActionPerformed( Hoofdscherm.java:177)
at view.Hoofdscherm.access$700(Hoofdscherm.java:14)
at view.Hoofdscherm$8.actionPerformed(Hoofdscherm.jav a:99)
at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed (AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed (DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultB uttonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.jav a:6267)
at javax.swing.JComponent.processMouseEvent(JComponen t.java:3267)
at java.awt.Component.processEvent(Component.java:603 2)
at java.awt.Container.processEvent(Container.java:204 1)
at java.awt.Component.dispatchEventImpl(Component.jav a:4630)
at java.awt.Container.dispatchEventImpl(Container.jav a:2099)
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.LightweightDispatcher.retargetMouseEvent( Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(C ontainer.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Conta iner.java:4168)
at java.awt.Container.dispatchEventImpl(Container.jav a:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478 )
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 599)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:122)
BUILD SUCCESSFUL (total time: 4 seconds)

[aborgeld]

when i do this the problem is almost solved:

int aantalStudenten = Database.getAmountResultSet(r) - 1;

I get the last 3 records. Only where is my first record
'3', 'Kezer', '1991-06-19', '1', 'i', '1'
'4', 'Oosting, '1968-06-06', '1', 'bi', '2'
'5', 'Bruins', '1970-08-08', '0', 'idm', '4'

First record in the database i'm not getting:
'2', 'Borgeld', '1978-05-19', '1', 'i', '1'

I only get:
3
4
5

[aborgeld]

Issue Solved. Thanks for getting me in the right direction.

Solution:

public static Student[] getAllStudenten() {
    return getStudentCode ("select * from student order by code");
  }



    private static Student[] getStudentCode(String query){

    ResultSet r = Database.executeSelectQuery(query);

    int aantalStudenten = Database.getAmountResultSet(r);
    Student[] studenten = new Student[aantalStudenten];

   try {
   
        int teller  = 0;

   {
        while (teller < aantalStudenten) {
            
            Student value = new Student();
            value.code = r.getInt("code");
            value.setAchternaam(r.getString("achternaam"));
            //System.out.println("Student: getStudenten: betaald " + r.getInt("betaald"));
            value.setBetaald(r.getInt("betaald"));

             studenten[teller] = value;
             teller++;
             r.next();
         }
       }
      }