NullPointerException - Cannot get the value from variable f_cashGiven

Question

In SubCheckout.java (a POS), what I want is when Payment button (f_cashPayment) is pressed, the action "Cash" is performed, get the value from Cash Given (f_cashGiven), do the subtraction and post the value as Cash Return (f_cashReturn). The code is filled in actionPerformed. But I cannot get the value by using f_cashGiven.getValue() from VNumber class. It returns NULL. This should be quite straight forward, but I do not know what is wrong. Please help!
Enclosed please find the source code of SubCheckout.java and VNumber.java
This is the code of SubCheckout.java :
* The contents of this file are subject to the   Compiere License  Version 1.1
* ("License"); You may not use this file except in compliance with the License
* You may obtain a copy of the License at http://www.compiere.org/license.html
* Software distributed under the License is distributed on an  "AS IS"  basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
* the specific language governing rights and limitations under the License.
* The Original Code is Compiere ERP & CRM Smart Business Solution. The Initial
* Developer of the Original Code is Jorg Janke. Portions created by Jorg Janke
* are Copyright (C) 1999-2005 Jorg Janke.
* All parts are Copyright (C) 1999-2005 ComPiere, Inc.  All Rights Reserved.
* Contributor(s): ______________________________________.
package org.compiere.pos;
import java.awt.*;
import java.awt.event.*;
import java.math.BigDecimal;
import javax.swing.border.*;
import org.compiere.grid.ed.*;
import org.compiere.swing.*;
import org.compiere.util.*;
*     POS Checkout Sub Panel
*  @author Jorg Janke
*  @version $Id: SubCheckout.java,v 1.3 2005/03/11 20:28:22 jjanke Exp $
public class SubCheckout extends PosSubPanel implements ActionListener
      *      Constructor
      *     @param posPanel POS Panel
     public SubCheckout (PosPanel posPanel)
          super (posPanel);
     }     //     PosSubCheckout
     private CButton f_register = null;
     private CButton f_summary = null;
     private CButton f_process = null;
     private CButton f_print = null;
     private CLabel f_lcreditCardNumber = null;
     private CTextField f_creditCardNumber = null;
     private CLabel f_lcreditCardExp = null;
     private CTextField f_creditCardExp = null;
     private CLabel f_lcreditCardVV = null;
     private CTextField f_creditCardVV = null;
     private CButton f_cashPayment = null;
     private CLabel f_lcashGiven = null;
     private VNumber f_cashGiven = null;
     private CLabel f_lcashReturn = null;
     private VNumber f_cashReturn = null;
     private CButton f_creditPayment = null;
     /**     Logger               */
     private static CLogger log = CLogger.getCLogger(SubCheckout.class);
      *      Initialize
     public void init()
          //     Title
          TitledBorder border = new TitledBorder(Msg.getMsg(Env.getCtx(), "Checkout"));
          setBorder(border);
          //     Content
          setLayout(new GridBagLayout());
          GridBagConstraints gbc = new GridBagConstraints();
          gbc.insets = INSETS2;
          //     --     0
          gbc.gridx = 0;
          f_register = createButtonAction("Register", null);
          gbc.gridy = 0;
          add (f_register, gbc);
          f_summary = createButtonAction("Summary", null);
          gbc.gridy = 1;
          add (f_summary, gbc);
          f_process = createButtonAction("Process", null);
          gbc.gridy = 2;
          add (f_process, gbc);
          f_print = createButtonAction("Print", null);
          gbc.gridy = 3;
          add (f_print, gbc);
          //     --     1 -- Cash
          gbc.gridx = 1;
          gbc.gridheight = 2;
          gbc.fill = GridBagConstraints.BOTH;
          gbc.weightx = .1;
          CPanel cash = new CPanel(new GridBagLayout());
          cash.setBorder(new TitledBorder(Msg.getMsg(Env.getCtx(), "Cash")));
          gbc.gridy = 0;
          add (cash, gbc);
          GridBagConstraints gbc0 = new GridBagConstraints();
          gbc0.insets = INSETS2;
          gbc0.anchor = GridBagConstraints.WEST;
          f_lcashGiven = new CLabel(Msg.getMsg(Env.getCtx(),"CashGiven"));
          cash.add (f_lcashGiven, gbc0);
          f_cashGiven = new VNumber("CashGiven", false, false, true, DisplayType.Amount,
               Msg.translate(Env.getCtx(), "CashGiven"));
          f_cashGiven.addActionListener(this);
          f_cashGiven.setColumns(10, 25);
          cash.add (f_cashGiven, gbc0);
          f_cashGiven.setValue(Env.ZERO);
          f_lcashReturn = new CLabel(Msg.getMsg(Env.getCtx(),"CashReturn"));
          cash.add (f_lcashReturn, gbc0);
          f_cashReturn = new VNumber("CashReturn", false, true, false, DisplayType.Amount,
               "CashReturn");
          f_cashReturn.setColumns(10, 25);
          cash.add (f_cashReturn, gbc0);
          f_cashReturn.setValue(Env.ZERO);
          f_cashPayment = createButtonAction("Payment", null);
          f_cashPayment.setActionCommand("Cash");
          gbc0.anchor = GridBagConstraints.EAST;
          gbc0.weightx = 0.1;
          cash.add (f_cashPayment, gbc0);
          //     --     1 -- Creditcard
          CPanel creditcard = new CPanel(new GridBagLayout());
          creditcard.setBorder(new TitledBorder(Msg.translate(Env.getCtx(), "CreditCardType")));
          gbc.gridy = 2;
          add (creditcard, gbc);
          GridBagConstraints gbc1 = new GridBagConstraints();
          gbc1.insets = INSETS2;
          gbc1.anchor = GridBagConstraints.WEST;
          gbc1.gridx = 0;
          gbc1.gridy = 0;
          f_lcreditCardNumber = new CLabel(Msg.translate(Env.getCtx(), "CreditCardNumber"));
          creditcard.add (f_lcreditCardNumber, gbc1);
          gbc1.gridy = 1;
          f_creditCardNumber = new CTextField(18);
          creditcard.add (f_creditCardNumber, gbc1);
          gbc1.gridx = 1;
          gbc1.gridy = 0;
          f_lcreditCardExp = new CLabel(Msg.translate(Env.getCtx(),"CreditCardExp"));
          creditcard.add (f_lcreditCardExp, gbc1);
          gbc1.gridy = 1;
          f_creditCardExp = new CTextField(5);
          creditcard.add (f_creditCardExp, gbc1);
          gbc1.gridx = 2;
          gbc1.gridy = 0;
          f_lcreditCardVV = new CLabel(Msg.translate(Env.getCtx(), "CreditCardVV"));
          creditcard.add (f_lcreditCardVV, gbc1);
          gbc1.gridy = 1;
          f_creditCardVV = new CTextField(5);
          creditcard.add (f_creditCardVV, gbc1);
          gbc1.gridx = 3;
          gbc1.gridy = 0;
          gbc1.gridheight = 2;
          f_creditPayment = createButtonAction("Payment", null);
          f_creditPayment.setActionCommand("CreditCard");
          gbc1.anchor = GridBagConstraints.EAST;
          gbc1.weightx = 0.1;
          creditcard.add (f_creditPayment, gbc1);
     }     //     init
      *      Get Panel Position
     public GridBagConstraints getGridBagConstraints()
          GridBagConstraints gbc = super.getGridBagConstraints();
          gbc.gridx = 0;
          gbc.gridy = 3;
          return gbc;
     }     //     getGridBagConstraints
      *      Dispose - Free Resources
     public void dispose()
          super.dispose();
     }     //     dispose
      *      Action Listener
      *     @param e event
     public void actionPerformed (ActionEvent e)
          String action = e.getActionCommand();
          if (action == null || action.length() == 0)
               return;
          log.info( "PosSubCheckout - actionPerformed: " + action);
          if (e.getSource() == f_cashGiven) {
               f_cashGiven.setValue(f_cashGiven.getValue());
               System.out.println("f_cashGiven"+f_cashGiven.getDisplay());
          //     Register
          //     Summary
          //     Print
          if (action.equals("Cash")) {
               BigDecimal CashGiven, GrandTotal, CashReturn;
               System.out.println("Cash given is "+f_cashGiven.getDisplay());
               CashGiven = (BigDecimal)f_cashGiven.getValue();
               GrandTotal = (BigDecimal)p_posPanel.f_curLine.getOrder().getGrandTotal();
               CashReturn = CashGiven.subtract(GrandTotal);
               f_cashReturn.setValue(CashReturn);
          //     Cash (Payment)
          //     CreditCard (Payment)
     }     //     actionPerformed
}     //     PosSubCheckoutThis is the code of VNumber.java :
* The contents of this file are subject to the   Compiere License  Version 1.1
* ("License"); You may not use this file except in compliance with the License
* You may obtain a copy of the License at http://www.compiere.org/license.html
* Software distributed under the License is distributed on an  "AS IS"  basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
* the specific language governing rights and limitations under the License.
* The Original Code is Compiere ERP & CRM Smart Business Solution. The Initial
* Developer of the Original Code is Jorg Janke. Portions created by Jorg Janke
* are Copyright (C) 1999-2005 Jorg Janke.
* All parts are Copyright (C) 1999-2005 ComPiere, Inc.  All Rights Reserved.
* Contributor(s): ______________________________________.
package org.compiere.grid.ed;
import java.awt.*;
import java.awt.event.*;
import java.beans.*;
import java.math.*;
import java.text.*;
import java.util.logging.*;
import javax.swing.*;
import javax.swing.text.*;
import org.compiere.apps.*;
import org.compiere.model.*;
import org.compiere.swing.*;
import org.compiere.util.*;
*     Number Control
*      @author      Jorg Janke
*      @version      $Id: VNumber.java,v 1.41 2005/09/03 01:57:16 jjanke Exp $
public final class VNumber extends JComponent
     implements VEditor, ActionListener, KeyListener, FocusListener
     /**     Number of Columns (12)          */
     public final static int SIZE = 12;
      *  IDE Bean Constructor
     public VNumber()
          this("Number", false, false, true, DisplayType.Number, "Number");
     }   //  VNumber
      *     Create right aligned Number field.
      *     no popup, if WindowNo == 0 (for IDs)
      *  @param columnName column name
      *  @param mandatory mandatory
      *  @param isReadOnly read only
      *  @param isUpdateable updateable
      *  @param displayType display type
      *  @param title title
     public VNumber(String columnName, boolean mandatory, boolean isReadOnly, boolean isUpdateable,
          int displayType, String title)
          super();
          super.setName(columnName);
          m_columnName = columnName;
          m_title = title;
          setDisplayType(displayType);
          LookAndFeel.installBorder(this, "TextField.border");
          this.setLayout(new BorderLayout());
//          this.setPreferredSize(m_text.getPreferredSize());          //     causes r/o to be the same length
//          int height = m_text.getPreferredSize().height;
//          setMinimumSize(new Dimension (30,height));
          //     ***     Text     ***
          m_text.setBorder(null);
          m_text.setHorizontalAlignment(JTextField.TRAILING);
          m_text.addKeyListener(this);
          m_text.addFocusListener(this);
          //     Background
          setMandatory(mandatory);
          this.add(m_text, BorderLayout.CENTER);
          //     ***     Button     ***
          m_button.setIcon(Env.getImageIcon("Calculator10.gif"));
          m_button.setMargin(new Insets(0, 0, 0, 0));
          m_button.setFocusable(false);
          m_button.addActionListener(this);
          this.add (m_button, BorderLayout.EAST);
          //     Prefereed Size
          this.setPreferredSize(this.getPreferredSize());          //     causes r/o to be the same length
          //  Size
          setColumns(SIZE, CComboBox.FIELD_HIGHT-4);     
          //     ReadWrite
          if (isReadOnly || !isUpdateable)
               setReadWrite(false);
          else
               setReadWrite(true);
     }     //     VNumber
      *  Dispose
     public void dispose()
          m_text = null;
          m_button = null;
          m_mField = null;
     }   //  dispose
      *     Set Document
      *  @param doc document
     protected void setDocument(Document doc)
          m_text.setDocument(doc);
     }     //     getDocument
     private String               m_columnName;
     protected int               m_displayType;     //  Currency / UoM via Context
     private DecimalFormat     m_format;
     private String               m_title;
     private boolean               m_setting;
     private String               m_oldText;
     private String               m_initialText;
     private boolean               m_rangeSet = false;
     private Double               m_minValue;
     private Double               m_maxValue;
     private boolean               m_modified = false;
     /**  The Field                  */
     private CTextField          m_text = new CTextField(SIZE);     //     Standard
     /** The Button                  */
     private CButton              m_button = new CButton();
     private MField          m_mField = null;
     /**     Logger               */
     private static CLogger log = CLogger.getCLogger(VNumber.class);
      *      Set no of Columns
      *     @param columns columns
     public void setColumns (int columns, int height)
          m_text.setPreferredSize(null);
          m_text.setColumns(columns);
          Dimension size = m_text.getPreferredSize();
          if (height > size.height)               //     default 16
               size.height = height;
          if (CComboBox.FIELD_HIGHT-4 > size.height)
               size.height = VLookup.FIELD_HIGHT-4;
          this.setPreferredSize(size);          //     causes r/o to be the same length
          this.setMinimumSize(new Dimension (columns*10, size.height));
          m_button.setPreferredSize(new Dimension(size.height, size.height));
     }     //     setColumns
      *     Set Range with min & max
      *  @param minValue min value
      *  @param maxValue max value
      *     @return true, if accepted
     public boolean setRange(Double minValue, Double maxValue)
          m_rangeSet = true;
          m_minValue = minValue;
          m_maxValue = maxValue;
          return m_rangeSet;
     }     //     setRange
      *     Set Range with min & max = parse US style number w/o Gouping
      *  @param minValue min value
      *  @param maxValue max value
      *  @return true if accepted
     public boolean setRange(String minValue, String maxValue)
          if (minValue == null || maxValue == null)
               return false;
          try
               m_minValue = Double.valueOf(minValue);
               m_maxValue = Double.valueOf(maxValue);
          catch (NumberFormatException nfe)
               return false;
          m_rangeSet = true;
          return m_rangeSet;
     }     //     setRange
      *  Set and check DisplayType
      *  @param displayType display type
     public void setDisplayType (int displayType)
          m_displayType = displayType;
          if (!DisplayType.isNumeric(displayType))
               m_displayType = DisplayType.Number;
          m_format = DisplayType.getNumberFormat(displayType);
          m_text.setDocument (new MDocNumber(displayType, m_format, m_text, m_title));
     }   //  setDisplayType
      *     Set ReadWrite
      *  @param value value
     public void setReadWrite (boolean value)
          if (m_text.isReadWrite() != value)
               m_text.setReadWrite(value);
          if (m_button.isReadWrite() != value)
               m_button.setReadWrite(value);
          //     Don't show button if not ReadWrite
          if (m_button.isVisible() != value)
               m_button.setVisible(value);
     }     //     setReadWrite
      *     IsReadWrite
      *  @return true if rw
     public boolean isReadWrite()
          return m_text.isReadWrite();
     }     //     isReadWrite
      *     Set Mandatory (and back bolor)
      *  @param mandatory mandatory
     public void setMandatory (boolean mandatory)
          m_text.setMandatory(mandatory);
     }     //     setMandatory
      *     Is it mandatory
      *  @return true if mandatory
     public boolean isMandatory()
          return m_text.isMandatory();
     }     //     isMandatory
      *     Set Background
      *  @param color color
     public void setBackground(Color color)
          m_text.setBackground(color);
     }     //     setBackground
      *     Set Background
      *  @param error error
     public void setBackground (boolean error)
          m_text.setBackground(error);
     }     //     setBackground
      *  Set Foreground
      *  @param fg foreground
     public void setForeground(Color fg)
          m_text.setForeground(fg);
     }   //  setForeground
      *     Set Editor to value
      *  @param value value
     public void setValue(Object value)
          log.finest("Value=" + value);
          if (value == null)
               m_oldText = "";
          else
               m_oldText = m_format.format(value);
          //     only set when not updated here
          if (m_setting)
               return;
          m_text.setText (m_oldText);
          m_initialText = m_oldText;
          m_modified = false;
     }     //     setValue
      *  Property Change Listener
      *  @param evt event
     public void propertyChange (PropertyChangeEvent evt)
          if (evt.getPropertyName().equals(org.compiere.model.MField.PROPERTY))
               setValue(evt.getNewValue());
     }   //  propertyChange
      *     Return Editor value
      *  @return value value (big decimal or integer)
     public Object getValue()
          if (m_text == null || m_text.getText() == null || m_text.getText().length() == 0)
               return null;
          String value = m_text.getText();
          //     return 0 if text deleted
          if (value == null || value.length() == 0)
               if (!m_modified)
                    return null;
               if (m_displayType == DisplayType.Integer)
                    return new Integer(0);
               return Env.ZERO;
          if (value.equals(".") || value.equals(",") || value.equals("-"))
               value = "0";
          try
               Number number = m_format.parse(value);
               value = number.toString();      //     converts it to US w/o thousands
               BigDecimal bd = new BigDecimal(value);
               if (m_displayType == DisplayType.Integer)
                    return new Integer(bd.intValue());
               if (bd.signum() == 0)
                    return bd;
               return bd.setScale(m_format.getMaximumFractionDigits(), BigDecimal.ROUND_HALF_UP);
          catch (Exception e)
               log.log(Level.SEVERE, "Value=" + value, e);
          if (m_displayType == DisplayType.Integer)
               return new Integer(0);
          return Env.ZERO;
     }     //     getValue
      *  Return Display Value
      *  @return value
     public String getDisplay()
          return m_text.getText();
     }   //  getDisplay
      *      Get Title
      *     @return title
     public String getTitle()
          return m_title;
     }     //     getTitle
      *      Plus - add one.
      *      Also sets Value
      *     @return new value
     public Object plus()
          Object value = getValue();
          if (value == null)
               if (m_displayType == DisplayType.Integer)
                    value = new Integer(0);
               else
                    value = Env.ZERO;
          //     Add
          if (value instanceof BigDecimal)
               value = ((BigDecimal)value).add(Env.ONE);
          else
               value = new Integer(((Integer)value).intValue() + 1);
          setValue(value);
          return value;
     }     //     plus
      *      Minus - subtract one, but not below minimum.
      *      Also sets Value
      *     @param minimum minimum
      *     @return new value
     public Object minus (int minimum)
          Object value = getValue();
          if (value == null)
               if (m_displayType == DisplayType.Integer)
                    value = new Integer(minimum);
               else
                    value = new BigDecimal(minimum);
               setValue(value);
               return value;
          //     Subtract
          if (value instanceof BigDecimal)
               BigDecimal bd = ((BigDecimal)value).subtract(Env.ONE);
               BigDecimal min = new BigDecimal(minimum);
               if (bd.compareTo(min) < 0)
                    value = min;
               else
                    value = bd;
          else
               int i = ((Integer)value).intValue();
               i--;
               if (i < minimum)
                    i = minimum;
               value = new Integer(i);
          setValue(value);
          return value;
     }     //     minus
      *     Action Listener
      *  @param e event
     public void actionPerformed (ActionEvent e)
          log.config(e.getActionCommand());
          if (ValuePreference.NAME.equals(e.getActionCommand()))
               if (MRole.getDefault().isShowPreference())
                    ValuePreference.start (m_mField, getValue());
               return;
          if (e.getSource() == m_button)
               m_button.setEnabled(false);
               String str = startCalculator(this, m_text.getText(), m_format, m_displayType, m_title);
               m_text.setText(str);
               m_button.setEnabled(true);
               try
                    fireVetoableChange (m_columnName, m_oldText, getValue());
               catch (PropertyVetoException pve)     {}
               m_text.requestFocus();
     }     //     actionPerformed
      *     Key Listener Interface
      *  @param e event
     public void keyTyped(KeyEvent e)    {}
     public void keyPressed(KeyEvent e)  {}
      *     Key Listener.
      *          - Escape           - Restore old Text
      *          - firstChange     - signal change
      *  @param e event
     public void keyReleased(KeyEvent e)
          log.finest("Key=" + e.getKeyCode() + " - " + e.getKeyChar()
                       + " -> " + m_text.getText());
          //  ESC
          if (e.getKeyCode() == KeyEvent.VK_ESCAPE)
               m_text.setText(m_initialText);
          m_modified = true;
          m_setting = true;
          try
               if (e.getKeyCode() == KeyEvent.VK_ENTER)     //     10
                    fireVetoableChange (m_columnName, m_oldText, getValue());
                    fireActionPerformed();
               else     //     indicate change
                    fireVetoableChange (m_columnName, m_oldText, null);     
          catch (PropertyVetoException pve)     {}
          m_setting = false;
     }     //     keyReleased
      *     Focus Gained
      *  @param e event
     public void focusGained (FocusEvent e)
          if (m_text != null)
               m_text.selectAll();
     }     //     focusGained
      *     Data Binding to MTable (via GridController.vetoableChange).
      *  @param e event
     public void focusLost (FocusEvent e)
     //          log.finest(e.toString());
          //     APanel - Escape
          if (e.getOppositeComponent() instanceof AGlassPane)
               m_text.setText(m_initialText);
               return;
          try
               fireVetoableChange (m_columnName, m_initialText, getValue());
               fireActionPerformed();
          catch (PropertyVetoException pve)     {}
     }   //  focusLost
      *     Invalid Entry - Start Calculator
      *  @param jc parent
      *  @param value value
      *  @param format format
      *  @param displayType display type
      *  @param title title
      *  @return value
     public static String startCalculator(Container jc, String value,
          DecimalFormat format, int displayType, String title)
          log.config("Value=" + value);
          BigDecimal startValue = new BigDecimal(0.0);
          try
               if (value != null && value.length() > 0)
                    Number number = format.parse(value);
                    startValue = new BigDecimal (number.toString());
          catch (ParseException pe)
               log.info("InvalidEntry - " + pe.getMessage());
          //     Find frame
          Frame frame = Env.getFrame(jc);
          //     Actual Call
          Calculator calc = new Calculator(frame, title,
               displayType, format, startValue);
          AEnv.showCenterWindow(frame, calc);
          BigDecimal result = calc.getNumber();
          log.config( "Result=" + result);
          calc = null;
          if (result != null)
               return format.format(result);
          else
               return value;          //     original value
     }     //     startCalculator
      *  Set Field/WindowNo for ValuePreference
      *  @param mField field
     public void setField (MField mField)
          m_mField = mField;
          if (m_mField != null
               && MRole.getDefault().isShowPreference())
               ValuePreference.addMenu (this, popupMenu);
     }   //  setField
      *      Remove Action Listner
      *      @param l Action Listener
     public void removeActionListener(ActionListener l)
          listenerList.remove(ActionListener.class, l);
     }     //     removeActionListener
      *      Add Action Listner
      *      @param l Action Listener
     public void addActionListener(ActionListener l)
          listenerList.add(ActionListener.class, l);
     }     //     addActionListener
      *      Fire Action Event to listeners
     protected void fireActionPerformed()
          int modifiers = 0;
          AWTEvent currentEvent = EventQueue.getCurrentEvent();
          if (currentEvent instanceof InputEvent)
               modifiers = ((InputEvent)currentEvent).getModifiers();
          else if (currentEvent instanceof ActionEvent)
               modifiers = ((ActionEvent)currentEvent).getModifiers();
          ActionEvent ae = new ActionEvent (this, ActionEvent.ACTION_PERFORMED,
               "VNumber", EventQueue.getMostRecentEventTime(), modifiers);
          // Guaranteed to return a non-null array
          Object[] listeners = listenerList.getListenerList();
          // Process the listeners last to first, notifying those that are interested in this event
          for (int i = listeners.length-2; i>=0; i-=2)
               if (listeners==ActionListener.class)
                    ((ActionListener)listeners[i+1]).actionPerformed(ae);
     }     //     fireActionPerformed
}     //     VNumber

Answer 1

If getValue() returns null, you need to trace the execution of the code and figure out which sequence of code is leading to the return of null. This method looks complex - a lot of if statements. If you do not have a debugger, put System.out.println statements inside the method to figure out what's going on.