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  1. #1
    warship is offline Member
    Join Date
    Jul 2007
    Posts
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    Unhappy NullPointerException problem

    hello.
    i am trying to log on to the video library system that i just developed. when i type "Administrator" in the username text field and 0 in the password field and press OK i get a lot of NullPointerException problems (the appropriate pieces of code are shown below). i had to press End on the jGRASP console in order to end the program. how can this problem be solved?

    Java Code:
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    import javax.swing.border.*;
     
    public class HomeEntertainment extends JPanel implements ActionListener{
       private JTabbedPane jtp = new JTabbedPane();
       private JPanel cP1 = new JPanel();
       private JPanel cP2 = new JPanel();
       private JPanel cP3 = new JPanel();
       private JPanel cP4 = new JPanel();
       private JPanel bP1 = new JPanel();
       private JPanel bP2 = new JPanel();
       private JPanel bP3 = new JPanel();
       private JPanel bP4 = new JPanel();
       private JButton jbAdministratorLogOn = new JButton("Log On");
       private JButton jbNewUserRegister = new JButton("Register");
       private JButton jbExistingUserLogOn = new JButton("Log On");
       private JButton jbExitTheSystem = new JButton("Exit the system");
    	
       public HomeEntertainment(){
          cP1.setLayout(new BorderLayout());
          cP2.setLayout(new BorderLayout());
          cP3.setLayout(new BorderLayout());
          cP4.setLayout(new BorderLayout());
          bP1.setBorder(new TitledBorder("Make a choice"));
          bP2.setBorder(new TitledBorder("Make a choice"));
          bP3.setBorder(new TitledBorder("Make a choice"));
          bP4.setBorder(new TitledBorder("Make a choice"));
          bP1.add(jbAdministratorLogOn);
          bP2.add(jbNewUserRegister);
          bP3.add(jbExistingUserLogOn);
          bP4.add(jbExitTheSystem);
          cP1.add(bP1, BorderLayout.SOUTH);
          cP2.add(bP2, BorderLayout.SOUTH);
          cP3.add(bP3, BorderLayout.SOUTH);
          cP4.add(bP4, BorderLayout.SOUTH);
          jtp.addTab("Administrator", cP1);
          jtp.addTab("New User", cP2);
          jtp.addTab("Existing User", cP3);
          jtp.addTab("Exit the system", cP4);
    		
          JFrame jf = new JFrame("Home Entertainment");		
          jf.getContentPane().add(jtp, BorderLayout.CENTER);
          jf.setSize(500, 500);
          jf.setVisible(true);
    		
          jbAdministratorLogOn.addActionListener(this);
          jbNewUserRegister.addActionListener(this);
          jbExistingUserLogOn.addActionListener(this);
          jbExitTheSystem.addActionListener(this);
       }
    	
       public void actionPerformed(ActionEvent e){
          if(e.getSource() == jbAdministratorLogOn){
             LogOn logOn = new LogOn();
             logOn.setVisible(true);
          }
          if(e.getSource() == jbNewUserRegister){
             RegistrationForm r = new RegistrationForm();
             r.setVisible(true);
          }
          if(e.getSource() == jbExistingUserLogOn){ 
             LogOn logOn = new LogOn();
             logOn.setVisible(true);
          }
          if(e.getSource() == jbExitTheSystem){ 
             System.exit(0);
          }
       }
    	
       public static void main(String[] args){
          new HomeEntertainment();
       }
    }
    
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
     
    public class LogOn extends JFrame{
       JPanel pnlBody, pnlFooter;
       JLabel unLabel = new JLabel("Username: ");
       JLabel pwLabel = new JLabel("Password: "); 
       JTextField jtfUN = new JTextField(20);
       JPasswordField jtfPW = new JPasswordField(20);
       JButton jbOK = new JButton("OK");
       JButton jbCancel = new JButton("Cancel");
       Container contentpane;
    	
       public LogOn(){
          super("Welcome to Home Entertainment");
          contentpane = getContentPane();
          contentpane.setLayout(new BorderLayout());
          pnlBody = new JPanel();
          pnlFooter = new JPanel();
          pnlBody.add(unLabel);
          pnlBody.add(jtfUN);
          pnlBody.add(pwLabel);
          pnlBody.add(jtfPW);
          pnlFooter.add(jbOK);
          pnlFooter.add(jbCancel);
          contentpane.add(pnlBody,BorderLayout.NORTH);
          contentpane.add(pnlFooter,BorderLayout.CENTER);
          pack();
          setVisible(true);
     
          jbOK.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                User u = new User();
                u.doLogOn();
                u.username = jtfUN.getText().trim();
                u.password = new String(jtfPW.getPassword());
                Administrator a = new Administrator();
                a.doLogOn();
                a.username = jtfUN.getText().trim();
                a.password = new String(jtfPW.getPassword());
                setVisible(false);
             }
          });
     
          jbCancel.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);
             }
          });
       }
    }
     
    class User{
       String username;
       String password;
       String[] userUsernameArray = {"Ann Smyth", "John Murphy"};
       String[] userPasswordArray = {"1", "2"};
    		
       public void doLogOn(){
          int i, j;
    	
          for(i = 0; i < userUsernameArray.length; i++){ 
             if(username.equals(userUsernameArray[i])){
                UserMainMenu umm = new UserMainMenu();
                umm.setVisible(true); 
             } 
             else{ 
                  JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
             } 
          } 
    		
          for(j = 0; j < userPasswordArray.length; j++){ 
             if(password.equals(userPasswordArray[j])){ 
                UserMainMenu umm = new UserMainMenu();
                umm.setVisible(true); 
             } 
             else{ 
                  JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
             } 
          }
       }
    }
     
    class Administrator{
       String username;
       String password;
       String[] adminUsernameArray = {"Administrator"};
       String[] adminPasswordArray = {"0"};
     
       public void doLogOn(){
          int k, l;
    	
          for(k = 0; k < adminUsernameArray.length; k++){ 
             if(username.equals(adminUsernameArray[k])){
                AdminMainMenu amm = new AdminMainMenu();
                amm.setVisible(true); 
             } 
             else{ 
                  JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
             } 
          } 
    		
          for(l = 0; l < adminPasswordArray.length; l++){ 
             if(password.equals(adminPasswordArray[l])){
                AdminMainMenu amm = new AdminMainMenu();
                amm.setVisible(true); 
             } 
             else{ 
                  JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
             } 
          } 
       } 
    }

  2. #2
    cecily is offline Member
    Join Date
    Jul 2007
    Posts
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    Default

    Can you paste the total exception that you got?

  3. #3
    warship is offline Member
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    Jul 2007
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    Default RE: NullPointerException problem

    hello cecily.
    here is the exception and the rest of the code.

    ----jGRASP exec: java HomeEntertainment

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at User.doLogOn(LogOn.java:71)
    at LogOn$1.actionPerformed(LogOn.java:42)
    at javax.swing.AbstractButton.fireActionPerformed(Unk nown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed (Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed (Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(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.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForHierar chy(Unknown 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)

    ----jGRASP: process aborted by user.

    Java Code:
    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
     
    public class AdminMainMenu extends JFrame{
       JPanel pnlBody;
       JButton btnOrderSystem = new JButton("Order System"); 
       JButton btnMaintenance = new JButton("Maintenance");
       JButton btnAdminLogOff = new JButton("Log Off"); 
       Container contentpane;
    	
       public AdminMainMenu(){
          super("Main Menu");
          contentpane = getContentPane();
          contentpane.setLayout(new BorderLayout());
          pnlBody = new JPanel();
          pnlBody.add(btnOrderSystem);
          pnlBody.add(btnMaintenance);
          pnlBody.add(btnAdminLogOff);
          contentpane.add(pnlBody,BorderLayout.CENTER);
          pack();
          setVisible(true);
    		
          btnOrderSystem.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);   
                //OrderSystem os = new OrderSystem();
                //os.setVisible(true);     
             }
          });
    		
          btnMaintenance.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);   
                //Maintenance m = new Maintenance();
                //m.setVisible(true);     
             }
          });
    		
          btnAdminLogOff.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                int result;
    				
                result = JOptionPane.showConfirmDialog(null, "Are you sure you want to log off?", null, JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
    				
                if(result == JOptionPane.YES_OPTION){
                   setVisible(false);
                }
             }
          });
       }
    }
    
    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
     
    public class UserMainMenu extends JFrame{
       JPanel pnlBody;
       JButton btnUserProductMenu = new JButton("Product Menu"); 
       JButton btnUserMemberMenu = new JButton("Member Menu"); 
       JButton btnUserRentalMenu = new JButton("Rental Menu"); 
       JButton btnUserLogOff = new JButton("Log Off"); 
       Container contentpane;
    	
       public UserMainMenu(){
          super("Main Menu");
          contentpane = getContentPane();
          contentpane.setLayout(new BorderLayout());
          pnlBody = new JPanel();
          pnlBody.add(btnUserProductMenu);
          pnlBody.add(btnUserMemberMenu);
          pnlBody.add(btnUserRentalMenu);
          pnlBody.add(btnUserLogOff);
          contentpane.add(pnlBody,BorderLayout.CENTER);
          pack();
          setVisible(true);
    		
          btnUserProductMenu.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);  
                //UserProductMenu upm = new UserProductMenu();
                //upm.setVisible(true);     
             }
          });
    		
          btnUserMemberMenu.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);  
                //UserMemberMenu umm = new UserMemberMenu();
                //umm.setVisible(true);   
             }
          });
    		
          btnUserRentalMenu.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);  
                //UserRentalMenu urm = new UserRentalMenu();
                //urm.setVisible(true);   
             }
          });
    		
          btnUserLogOff.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                int result;
    				
                result = JOptionPane.showConfirmDialog(null, "Are you sure you want to log off?", null, JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
    				
                if(result == JOptionPane.YES_OPTION){
                   setVisible(false);
                } 
             }
          });
       } 
    }

  4. #4
    warship is offline Member
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    Default RE: NullPointerException problem

    thanks for the reply.
    i moved the u.doLogon() + a.doLogon() after the username was set. when i tried to log on to my system the first time, 2 main menus appeared instead of one. i removed the for loop code. but when i tried to compile the video library menu program the second time, i got the following errors (both the errors and the modified LogOn.java program are shown below). i must have done something stupid now. should i put the for loops back into the code + modify the User and Administrator classes so that only one main menu appears when i log on to my system?

    ----jGRASP exec: javac -g E:\CP4B Project\HomeEntertainment.java

    LogOn.java:68: '.class' expected
    if(username.equals(userUsernameArray[]) && password.equals(userPasswordArray[])){
    ^
    LogOn.java:74: ')' expected
    }
    ^
    LogOn.java:75: illegal start of expression
    }
    ^
    LogOn.java:85: '.class' expected
    if(username.equals(adminUsernameArray[]) && password.equals(adminPasswordArray[])){
    ^
    LogOn.java:91: ')' expected
    }
    ^
    LogOn.java:92: illegal start of expression
    }
    ^
    LogOn.java:68: cannot find symbol
    symbol : class userUsernameArray
    location: class User
    if(username.equals(userUsernameArray[]) && password.equals(userPasswordArray[])){
    ^
    LogOn.java:68: unexpected type
    required: value
    found : class
    if(username.equals(userUsernameArray[]) && password.equals(userPasswordArray[])){
    ^
    LogOn.java:85: cannot find symbol
    symbol : class adminUsernameArray
    location: class Administrator
    if(username.equals(adminUsernameArray[]) && password.equals(adminPasswordArray[])){
    ^
    LogOn.java:85: unexpected type
    required: value
    found : class
    if(username.equals(adminUsernameArray[]) && password.equals(adminPasswordArray[])){
    ^
    10 errors

    ----jGRASP wedge2: exit code for process is 1.
    ----jGRASP: operation complete.

    Java Code:
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
     
    public class LogOn extends JFrame{
       JPanel pnlBody, pnlFooter;
       JLabel unLabel = new JLabel("Username: ");
       JLabel pwLabel = new JLabel("Password: "); 
       JTextField jtfUN = new JTextField(20);
       JPasswordField jtfPW = new JPasswordField(20);
       JButton jbOK = new JButton("OK");
       JButton jbCancel = new JButton("Cancel");
       Container contentpane;
    	
       public LogOn(){
          super("Welcome to Home Entertainment");
          contentpane = getContentPane();
          contentpane.setLayout(new BorderLayout());
          pnlBody = new JPanel();
          pnlFooter = new JPanel();
          pnlBody.add(unLabel);
          pnlBody.add(jtfUN);
          pnlBody.add(pwLabel);
          pnlBody.add(jtfPW);
          pnlFooter.add(jbOK);
          pnlFooter.add(jbCancel);
          contentpane.add(pnlBody,BorderLayout.NORTH);
          contentpane.add(pnlFooter,BorderLayout.CENTER);
          pack();
          setVisible(true);
     
          jbOK.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                User u = new User();
                u.username = jtfUN.getText().trim();
                u.doLogOn();
                u.password = new String(jtfPW.getPassword());
                Administrator a = new Administrator();
                a.username = jtfUN.getText().trim();
                a.doLogOn();
                a.password = new String(jtfPW.getPassword());
                setVisible(false);
             }
          });
     
          jbCancel.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
                setVisible(false);
             }
          });
       }
    }
     
    class User{
       String username;
       String password;
       String[] userUsernameArray = {"Ann Smyth", "John Murphy"};
       String[] userPasswordArray = {"1", "2"};
    		
       public void doLogOn(){
          if(username.equals(userUsernameArray[]) && password.equals(userPasswordArray[])){
             UserMainMenu umm = new UserMainMenu();
             umm.setVisible(true); 
          } 
          else{ 
               JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
          } 
       }
    }
     
    class Administrator{
       String username;
       String password;
       String[] adminUsernameArray = {"Administrator"};
       String[] adminPasswordArray = {"0"};
     
       public void doLogOn(){
          if(username.equals(adminUsernameArray[]) && password.equals(adminPasswordArray[])){
             AdminMainMenu amm = new AdminMainMenu();
             amm.setVisible(true); 
          }
          else{ 
               JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
          } 
       } 
    }

  5. #5
    mary is offline Member
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    Default

    Hi warship!!!
    I think that the problem is that you have to write the index in array
    username.equals(userUsernameArray[])
    for example
    Java Code:
    int index=1;
    username.equals(userUsernameArray[index])
    and check the doLogOn, the if statements are wrong

  6. #6
    Heather is offline Senior Member
    Join Date
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    Default

    check this code
    Java Code:
    import javax.swing.JOptionPane;
    
    class Administrator{
    String username;
    String password;
    String[] adminUsernameArray = {"Administrator"};
    String[] adminPasswordArray = {"0"};
    
    public void doLogOn(){
    if(username.equals(adminUsernameArray)
    && password.equals(adminPasswordArray)){
    AdminMainMenu amm = new AdminMainMenu();
    amm.setVisible(true);
    }
    else{
    JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
    }
    }
    }
    
    
    
    
    
    import javax.swing.JOptionPane;
    
    class User{
    String username;
    String password;
    String[] userUsernameArray = {"Ann Smyth", "John Murphy"};
    String[] userPasswordArray = {"1", "2"};
    
    public void doLogOn(){
    if(username.equals(userUsernameArray)
    && password.equals(userPasswordArray)){
    UserMainMenu umm = new UserMainMenu();
    umm.setVisible(true);
    }
    else{
    JOptionPane.showMessageDialog(null, "Error\n\nYou have entered an incorrect username and/or password\nPlease try again", null, JOptionPane.ERROR_MESSAGE);
    }
    }
    }

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