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![When I click the drop button, it shows me this: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at StudentInformation.RegistryDialog$ButtonListener.actionPerformed(RegistryDialog.java:184)]1

Here's the code:

import java.awt.*;
import javax.swing.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.table.*;
import javax.swing.event.*;

public class RegistryDialog extends JDialog {

//model
static Student selected = null;
Vector addedSbj = new Vector();
Subject slctdsbj;

//view
static JTable tbrsbj;
JScrollPane   sprsbj;
JLabel        lbrid   = new JLabel("id here");
JLabel        lbrnme  = new JLabel("name here");
JLabel        lbrcrs  = new JLabel("Course");
JLabel        lbryr   = new JLabel("Year");
SpinnerModel  mod     = new SpinnerNumberModel(1,1,4,1);
JSpinner      srryr   = new JSpinner(mod);
String[]      crs     = {"BS-CS","BS-IT","BS-IS"};
JComboBox     cbrcrs  = new JComboBox(crs);
JButton       btrok   = new JButton("Save");
JButton       btrcan  = new JButton("Close");
JButton       btradd  = new JButton("Add Subject");
JButton       btrdrp  = new JButton("Drop Subject");

RegistryDialog(JFrame parent, Student selectedStud) {
super(parent, true);
btrdrp.setEnabled(true);
selected = selectedStud;
setSbjTable();
setTitle("Student Registration Information");
Container cont = getContentPane();
EasierGridLayout layout = new EasierGridLayout();
cont.setLayout(layout);

cont.add(lbrid);        cont.add(lbrnme);
cont.add(btrok);        cont.add(btrcan);
cont.add(lbryr);        cont.add(srryr);
cont.add(lbrcrs);       cont.add(cbrcrs);
cont.add(sprsbj);       cont.add(btradd);
cont.add(btrdrp);

layout.setConstraints(lbrid,1,1,2,1);
layout.setConstraints(lbrnme,2,1,2,1);
layout.setConstraints(lbrcrs,3,1,1,1);
layout.setConstraints(lbryr,4,1,1,1);
layout.setConstraints(sprsbj,5,1,3,1);
layout.defineOwnConstraints(cbrcrs,3,2,1,1, 0,0, 0,17, 0,0,0,0);
layout.defineOwnConstraints(srryr,4,2,1,1, 0,0, 0,17, 0,0,0,0);
layout.defineOwnConstraints(btradd,4,2,2,1, 0,0, 0,13, 0,0,0,0);
layout.defineOwnConstraints(btrdrp,6,1,2,1, 0,0, 0,17, 0,0,0,0);
layout.defineOwnConstraints(btrok,6,3,1,1, 0,0, 0,13, 5,0,0,0);
layout.defineOwnConstraints(btrcan,7,3,1,1, 0,0, 0,13, 5,0,0,0);
fillFormWith(selected);

btrok.addActionListener(new ButtonListener());
btrcan.addActionListener(new ButtonListener());
btradd.addActionListener(new ButtonListener());
btrdrp.addActionListener(new ButtonListener());
tbrsbj.setModel(new SubjectModel());
ListSelectionModel tbModel = tbrsbj.getSelectionModel();
tbModel.addListSelectionListener(new SubjTableListener());

Toolkit thKit = getToolkit();
Dimension wndSze = thKit.getScreenSize();
pack();

int wd = getWidth();
int ht = getHeight();
int x  = (int)((wndSze.getWidth()/2)-(wd/2));
int y  = (int)((wndSze.getHeight()/2)-(ht/2));
setBounds(x,y,wd,ht);

//setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
//fill up for with necessary information.
private void fillFormWith(Student thisStudent){
Person temp = new Person(thisStudent.getFirstName(),
                         thisStudent.getLastName(),
                         thisStudent.getMiddleName());
lbrnme.setText("Full Name:     "+temp);
lbrid.setText("ID Number:     "+thisStudent.getIdNumber());
String stdCourse = thisStudent.getCourse();
int index = -1;
if(stdCourse.trim().equals("BS-CS"))
  index = 0;
else if(stdCourse.trim().equals("BS-IT"))
  index = 1;
else if(stdCourse.trim().equals("BS-IM"))
  index = 2;
cbrcrs.setSelectedIndex(index);
srryr.setValue(new Integer(thisStudent.getYear()));
}
private String getSCode(String thisToString){
  StringTokenizer str = new StringTokenizer(thisToString," -");
  String thisCode = str.nextToken().trim();
  return thisCode;
}
//setup table and table model
public void setSbjTable(){
  tbrsbj = new JTable(new SubjectModel());
  sprsbj = new JScrollPane(tbrsbj);
  tbrsbj.setPreferredScrollableViewportSize(new Dimension(550,150));
  tbrsbj.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
static class SubjectModel extends AbstractTableModel {
  private String[] columnNames = {"SUBJECT","UNITS","MAJOR?"};
  private Object[][] data = storeObject();

  private Object[][] storeObject(){
      Hashtable subj = selected.getSubjects();
      Set sKeys = subj.keySet();
      Vector keys = new Vector(sKeys);
      Collections.sort(keys);
      Object[][] temp = new Object[keys.size()][3];

      int a=0;
      for(Iterator i=keys.iterator();i.hasNext();a++){
      String thisKey = ""+i.next();
      Subject temp2 = (Subject)subj.get(thisKey);
      temp[a][0] = ""+temp2;
      temp[a][1] = ""+temp2.getUnits();
      if(temp2.isMajor())
        temp[a][2] = "YES";
      else
        temp[a][2] = "NO";
      }
      return temp;
    }
    public Object[][] getData(){
    return data;
    }
    public int getColumnCount() {
    return columnNames.length;
    }
    public int getRowCount() {
    return data.length;
    }
    public String getColumnName(int col) {
    return columnNames[col];
    }
    public Object getValueAt(int row, int col) {
    return data[row][col];
    }
    public boolean isCellEditable(int row, int col) {
    return false;
    }
  }

  //controller
  private class ButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent ev) {
      if(ev.getSource()==btrok){
        String crs = ""+cbrcrs.getSelectedItem();
        int yr = Integer.parseInt(""+srryr.getValue());
        selected.setCourse(crs);
        selected.setYear(yr);
        ViewElements.tb4grd.setModel(new StudRec.EnrModel());
        ViewElements.tb3stud.setModel(new StudRec.EnrModel());
        StudRec.writeFiles();       StudRec.readFiles();
        dispose();
      }
      if(ev.getSource()==btrcan){
        dispose();
      }
      if(ev.getSource()==btradd){
        AddSubjectDialog asbj = new AddSubjectDialog(new JFrame(),selected);
        asbj.show();
      }
      if(ev.getSource()==btrdrp){
          selected.dropSubject(slctdsbj.getCode());   
          ViewElements.currentSem.enrollStudent(selected);
          StudRec.writeFiles();     StudRec.readFiles();
          tbrsbj.setModel(new SubjectModel());
          System.out.println("subject dropped.");
      }
    }
  }
  private class SubjTableListener implements ListSelectionListener {
    public void valueChanged(ListSelectionEvent e) {
      if(e.getValueIsAdjusting()) return;
      ListSelectionModel lsm = (ListSelectionModel)e.getSource();
      if(lsm.isSelectionEmpty()) {
        btrdrp.setEnabled(false);
      }
      else {
        btrdrp.setEnabled(true);
        int selectedRow = lsm.getMinSelectionIndex();
        SubjectModel tempMod = new SubjectModel();
        String subj = ""+tempMod.getValueAt(selectedRow,0);
        String code = getSCode(subj);
        Hashtable ht = ViewElements.currentSem.getSubjectsOpen();
        slctdsbj = (Subject)ht.get(code);
     }
    }
  }
  private class MyWindowAdapter extends WindowAdapter {
    public void windowClosing(WindowEvent we) {
      dispose();

    }
  }
}

For line 184th, here's the code: selected.dropSubject(slctdsbj.getCode());

Neil
  • 1

0 Answers0