Thread: JComboBox null pointer Exception error

I can not figure out this JComboBox null pointer exception error. It happens when I attempt to use getSelectedItem() inside an ActionListener. The error doesn't actually initiate until I select an item with the combo box on the GUI when I run it. I don't understand why its null and after trying to figure it out for the past couple of hours I am stumped. where the combo box is created and initialized is highlighted in red. So is where the error is coming from.

import java.awt.event.*;
public class GUIController implements ActionListener
{
   //members
   private GUIView view;
 
 
   public GUIController()
   {
      view = new GUIView(this);
 
   }
   public static void main(String [] args) 
   {  
      //GUIView one = new GUIView();
      GUIController control = new GUIController();
   }
 
 
   public void actionPerformed (ActionEvent evt)
   {            
      //Clear all text input
      if (evt.getActionCommand().equals("Clear Input"))
      {
 
         view.getNameTxt().setText("");
         view.getSocialSecurityTxt().setText("");
         view.getMaritalStatusTxt().setText("");
         view.getSalaryTxt().setText("");
         view.getBossNameTxt().setText("");
         view.getDepartmentTxt().setText("");
         view.getTitleTxt().setText("");
         view.getBonusTxt().setText("");
 
      }
 
     [COLOR="Red"] //null exception error occurs here
      String input = (String)view.getEmployeeTypeBox().getSelectedItem();[/COLOR]
      if (input.equals("Worker"))
        view.getBonusTxt().setEditable(false);
 
   }
}

And the GUIView Class.......................

import java.awt.*;
import java.awt.event.*;
 
import javax.swing.*;
import javax.swing.event.AncestorListener;
public class GUIView extends JFrame
{
   //members
   private ActionListener controller;
 
   //size of Frame
   private static final int LENGTH = 700;
   private static final int WIDTH = 400;
   //size of input field bar
   private static final int BAR_SIZE = 10;
   //the final JPanel to be put onto the JFrame
  // private JPanel mainPanel;
 
   private JList employeeList;
 
   private String input;
 
 
   //=========For construction of input panel (West region of GUI)===
 
   //panels for construction of west GUI portion
   private JPanel gridInputPanel;
   private JPanel inputPanel;
   //Text fields for inputPanel
   private JTextField txtName;
   private JTextField txtSocialSecurity;
   private JTextField txtMaritalStatus;
   private JTextField txtSalary;
   private JTextField txtBossName;
   private JTextField txtDepartment;
   private JTextField txtTitle;
   private JTextField txtBonus;
   //labels for inputPanel
   private JLabel lblName;
   private JLabel lblSocialSecurity;
   private JLabel lblMaritalStatus;
   private JLabel lblSalary;
   private JLabel lblBossName;
   private JLabel lblDepartment;
   private JLabel lblTitle;
   private JLabel lblBonus;
 
   //JButtons
   private JButton addEmployee;
   private JButton clearInputButton;
 
 [COLOR="Red"]  //combo box is declared here
   private JComboBox employeeTypeBox;
   private  String[] employeeTypes = {"  ","Employee", "Manager", "Worker"};
   [/COLOR]
   //=========For construction of RIGTH region of GUI===
   private JPanel gridEmploySelection;
   //buttons
   private JButton sortListButton;
   private JButton clearListButton;
 
 
   //may want to add another argument for different actions
   GUIView(ActionListener ctr)
   {
      super("Employee GUI");
 
      controller = ctr;
      setSize(LENGTH, WIDTH);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setLayout(new GridLayout(1,4));
      //build the panels
      buildInputPanel();
      //for crdating sort button and list
      configureListComponents();
      buildSortPanel();
      //Add input Panel to frame
      add(gridInputPanel, BorderLayout.WEST);
      //Add listPanel to fram
      employeeList.setVisible(true);
      add(employeeList, BorderLayout.CENTER);
      add(gridEmploySelection, BorderLayout.EAST);
      setVisible(true);
   }
 
 
 
   private void configureListComponents()
   {
      employeeList = new JList();
      employeeList.setVisibleRowCount(3);
 
   }
 
 
 
   private void  buildSortPanel()
   {
       gridEmploySelection = new JPanel();
       gridEmploySelection.setLayout(new GridLayout(10,1));
      //buttons
       sortListButton = new JButton("Sort List");
       clearListButton = new JButton("Clear List");
       gridEmploySelection.add(sortListButton);
       gridEmploySelection.add(clearListButton);
       //add rodio buttons
   }
 
   /*================
      buildInputPanel():
      is responsible for construcing
      the West portion of the GUI.
      Any other Jpanels used to help build
      inputPanel will also be constructed 
      inside buildInputPanel() and then
      added to inputPanel.
    ==================
    */
   private void buildInputPanel()
   { 
      //initializes the JPanels
      gridInputPanel = new JPanel();
      gridInputPanel.setLayout(new GridLayout(18,2));
 
      [COLOR="Red"]//Combo box is initailized here
      JComboBox employeeTypeBox = new JComboBox(employeeTypes);
      //Add action to combo box
      employeeTypeBox.addActionListener(controller);[/COLOR]
 
      //initialize input text fields
      txtName = new JTextField(BAR_SIZE);
      txtSocialSecurity = new JTextField(BAR_SIZE);
      txtMaritalStatus = new JTextField(BAR_SIZE);
      txtSalary = new JTextField(BAR_SIZE);
      txtBossName = new JTextField(BAR_SIZE);
      txtDepartment = new JTextField(BAR_SIZE);
      txtTitle = new JTextField(BAR_SIZE);
      txtBonus = new JTextField(BAR_SIZE);
      //initialize txt label fields
      lblName = new JLabel("Name");
      lblSocialSecurity = new JLabel("Social Security");
      lblMaritalStatus = new JLabel("Marital Status");
      lblSalary = new JLabel("Salary");
      lblBossName = new JLabel("Boss Name");
      lblDepartment = new JLabel("Department");
      lblTitle = new JLabel("Title");
      lblBonus = new JLabel("Bonus");
 
 
      //======Add components to gridInputPanel==========
      addEmployee = new JButton("Add Employee");
      clearInputButton = new JButton("Clear Input");
 
      //adding txt input
      gridInputPanel.add(txtName);
      gridInputPanel.add(lblName);
      gridInputPanel.add(txtSocialSecurity);
      gridInputPanel.add(lblSocialSecurity);
      gridInputPanel.add(txtMaritalStatus);
      gridInputPanel.add(lblMaritalStatus);
      gridInputPanel.add(txtSalary);
      gridInputPanel.add(lblSalary);
      gridInputPanel.add(txtBossName);
      gridInputPanel.add(lblBossName);
      gridInputPanel.add(txtDepartment);
      gridInputPanel.add(lblDepartment);
      gridInputPanel.add(txtTitle);
      gridInputPanel.add(lblTitle);
      gridInputPanel.add(txtBonus);
      gridInputPanel.add(lblBonus);
 
 
      //Adding buttons and other stuff
      gridInputPanel.add(addEmployee);
      gridInputPanel.add(employeeTypeBox);
      gridInputPanel.add(clearInputButton);
 
 
      //adding actions to buttons
      clearInputButton.addActionListener(controller);
 
   }
 
   /*PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP
 
             ACCESSOR METHODS
 
    PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP*/
    public JTextField getNameTxt()
    {
       return txtName;
    }
 
    public JTextField getSocialSecurityTxt()
    {
       return txtSocialSecurity;
    }
 
    public JTextField getMaritalStatusTxt()
    {
       return txtMaritalStatus;
    }
 
    public JTextField getSalaryTxt()
    {
       return txtSalary;
    }
 
    public JTextField getBossNameTxt()
    {
       return txtBossName;
    }
 
    public JTextField getDepartmentTxt()
    {
       return txtDepartment;
    }
 
    public JTextField getTitleTxt()
    {
       return txtTitle;
    }
 
    public JTextField getBonusTxt()
    {
       return txtBonus;
    }
 
   [COLOR="Red"]//Combo box from GUI is accessed from Controller class here
    public JComboBox getEmployeeTypeBox()
    {
 
       return employeeTypeBox;
    }[/COLOR]

}





Thank you

With the following code:

JComboBox employeeTypeBox = new JComboBox(employeeTypes);

You are instantiating a local variable rather than your class variable, and so your class variable remains null. If you do the following you will instantiate the class variable instead.

employeeTypeBox = new JComboBox(employeeTypes);

Oh my gosh! Thanks! I didn't even realize that mistake even while looking for the problem. It works now. I can now finally continue with my program.


Thank you so much