java - Unstable program of JCheckbox in JTable -

i have gui hasjcheckbox in jtable table populated data database of vector.

i providing code below extracting data database:

 try {   preparedstatement pre = con.preparestatement("select * productinformation     customername='"+cust_name+"'");       vector<vector<string>> historyvector = new vector<vector<string>>();              rs = pre.executequery();     while(rs.next())     {     vector<string> history = new vector<string>();     serial_no=rs.getstring("serialnumber");      history.add(serial_no);     history.add(rs.getstring("model"));     history.add(rs.getstring("invoicenumber"));     history.add(rs.getstring("location"));           historyvector.add(history);       }             data=historyvector;              header = new vector<string>();      header.add("serial no");      header.add("model");     header.add("invoice no");      header.add("location");     header.add("asc");     header.add("amc");         amcascresult();     mainframe.add(amcascresult);     mainframe.remove(amc);     mainframe.validate();     mainframe.repaint();     mainframe.pack();         }         catch(exception e){             system.err.println(e);         } 

i experiencing problem when run program select jcheckbox returns null pointer exception. times runs expected.

my code inserting records table

 amcasc_table.setmodel(new javax.swing.table.defaulttablemodel(         data,header     ) {         boolean[] canedit = new boolean [] {             false, false, false, true, true         };          private static final long serialversionuid = 1l;          /*@override         public class getcolumnclass(int column) {         return getvalueat(0, column).getclass();         }*/         @override         public class getcolumnclass(int column) {             switch (column) {                 case 0:                     return string.class;                 case 1:                     return string.class;                 case 2:                     return string.class;                 case 3:                     return string.class;                 default:                     return boolean.class;             }         }          public boolean iscelleditable(int rowindex, int columnindex) {             return canedit [columnindex];         }     });     jscrollpane1.setviewportview(amcasc_table); 

and getting values of jcheckbox.

 (int = 0; <amcasc_table.getrowcount(); i++) {  boolean ischecked = (boolean) amcasc_table.getvalueat(i, 4);   if (ischecked) {     //get values of columns need.   string value = (string) amcasc_table.getvalueat(i, 0);   system.out.println(value);  } } 

what mistake have done , can me how overcome this?

sscce

     import java.awt.headlessexception;      import java.awt.event.actionevent;      import java.awt.event.keyevent;      import java.sql.*;      import java.text.dateformat;      import java.text.format;      import java.text.parseexception;      import java.text.simpledateformat;      import java.util.date;      import java.util.properties;      import java.util.vector;      import javax.mail.*;      import javax.mail.internet.internetaddress;      import javax.mail.internet.mimemessage;      import javax.swing.*;   public class combined { session session; jframe mainframe,mailframe; jpanel firstpane, newsales, confirmnewsales, checkserialno, producthistory, newcomplaint, newcomplaintentry; jpanel  confirmcomplaint,sendmail,generatereport,generatereportresult,amc,amcascresult,amcascconfirm; jmenubar menubar; jmenu menu; jmenuitem menuitem; jmenu submenu; jradiobuttonmenuitem rbmenuitem; jcheckboxmenuitem cbmenuitem; connection con,con1; statement st,st1; dateformat dateformat = new simpledateformat("dd/mm/yyyy"); format mmformat = new simpledateformat("mm"); dateformat yyformat = new simpledateformat("yy"); dateformat ddformat = new simpledateformat("dd"); string invoice_no; string serial_no; string model; string cust_name; string cust_location; string amc_status; date date_of_purchase; date amc_start_date; date amc_end_date; string amcend_date; string amcstart_date; buttonmodel amc_status_model; string query; resultset rs,rs1; date dateofpurchase; string date_ofpurchase; string query1; string eng_name; string problem_description; string contact_person; string contact_no; string calldate; string callmonth; string callyear; string callno; int inccallno; string lastcallno; string query3, query4, query5; string lastcalldate; string sinccallno; string db; string toaddress; string subject; string messagebody; string warrantystatus; vector<vector<string>> data;  vector<string> header;  string callstatus; int no_of_calls = 0;  public combined() {     connect();     framegen();  }  private void framegen() {     mainframe = new jframe("product maintenance , support software");     //create menu bar.     menubar = new jmenubar();      //build first menu.     menu = new jmenu("a menu");     menu.setmnemonic(keyevent.vk_a);     menu.getaccessiblecontext().setaccessibledescription(             "the menu in program has menu items");     menubar.add(menu);      //a group of jmenuitems     menuitem = new jmenuitem("a text-only menu item",             keyevent.vk_t);     menuitem.setaccelerator(keystroke.getkeystroke(             keyevent.vk_1, actionevent.alt_mask));     menuitem.getaccessiblecontext().setaccessibledescription(             "this doesn't anything");     menu.add(menuitem);      menuitem = new jmenuitem("both text , icon",             new imageicon("images/middle.gif"));     menuitem.setmnemonic(keyevent.vk_b);     menu.add(menuitem);      menuitem = new jmenuitem(new imageicon("images/middle.gif"));     menuitem.setmnemonic(keyevent.vk_d);     menu.add(menuitem);       //a group of radio button menu items     menu.addseparator();     buttongroup group = new buttongroup();     rbmenuitem = new jradiobuttonmenuitem("a radio button menu item");     rbmenuitem.setselected(true);     rbmenuitem.setmnemonic(keyevent.vk_r);     group.add(rbmenuitem);     menu.add(rbmenuitem);      rbmenuitem = new jradiobuttonmenuitem("another one");     rbmenuitem.setmnemonic(keyevent.vk_o);     group.add(rbmenuitem);     menu.add(rbmenuitem);      //a group of check box menu items     menu.addseparator();     cbmenuitem = new jcheckboxmenuitem("a check box menu item");     cbmenuitem.setmnemonic(keyevent.vk_c);     menu.add(cbmenuitem);      cbmenuitem = new jcheckboxmenuitem("another one");     cbmenuitem.setmnemonic(keyevent.vk_h);     menu.add(cbmenuitem);      //a submenu     menu.addseparator();     submenu = new jmenu("a submenu");     submenu.setmnemonic(keyevent.vk_s);      menuitem = new jmenuitem("an item in submenu");     menuitem.setaccelerator(keystroke.getkeystroke(             keyevent.vk_2, actionevent.alt_mask));     submenu.add(menuitem);      menuitem = new jmenuitem("another item");     submenu.add(menuitem);     menu.add(submenu);     //build second menu in menu bar.     menu = new jmenu("another menu");     menu.setmnemonic(keyevent.vk_n);     menu.getaccessiblecontext().setaccessibledescription(             "this menu nothing");     menubar.add(menu);      mainframe.setjmenubar(menubar);     firstpane();     mainframe.add(firstpane);     mainframe.pack();     mainframe.setvisible(true);     mainframe.setdefaultcloseoperation(3);     mainframe.setresizable(false);  }  /**  * @param args command line arguments  */ public static void main(string[] args) {     // todo code application logic here     combined com = new combined();  }  private void connect() {     try {         string driver = "sun.jdbc.odbc.jdbcodbcdriver";         class.forname(driver);          string db1 = "jdbc:odbc:solaris";         con = drivermanager.getconnection(db1);         st = con.createstatement();     } catch (classnotfoundexception | sqlexception ex) {         system.out.println("database connection failed");     } }    private void firstpane() {     firstpane = new jpanel();      addnewsales_button = new javax.swing.jbutton();     newcomplaint_button = new javax.swing.jbutton();     calllist_button = new javax.swing.jbutton();     generatereport_button = new javax.swing.jbutton();     serialnocheck_button = new javax.swing.jbutton();     solaris_logo = new javax.swing.jlabel();     support_label = new javax.swing.jlabel();     putamc_button = new javax.swing.jbutton();      firstpane.setbackground(new java.awt.color(255, 255, 255));      addnewsales_button.settext("add new sales entry");      addnewsales_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {            // addnewsales_buttonactionperformed(evt);         }     });      newcomplaint_button.settext("new complaint");     newcomplaint_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {            // newcomplaint_buttonactionperformed(evt);         }     });      calllist_button.settext("call list");     calllist_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {            // calllist_buttonactionperformed(evt);         }     });      generatereport_button.settext("generate report");     generatereport_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {             //generatereport_buttonactionperformed(evt);         }     });      serialnocheck_button.settext("serial number check");     serialnocheck_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {            // serialnocheck_buttonactionperformed(evt);         }     });      solaris_logo.seticon(new javax.swing.imageicon(getclass().getresource("/combined/image/solaris_logo.jpg"))); // noi18n      support_label.settext("support section");      putamc_button.settext("put amc");     putamc_button.addactionlistener(new java.awt.event.actionlistener() {          @override         public void actionperformed(java.awt.event.actionevent evt) {             putamc_buttonactionperformed(evt);         }     });      javax.swing.grouplayout layout = new javax.swing.grouplayout(firstpane);     firstpane.setlayout(layout);     layout.sethorizontalgroup(             layout.createparallelgroup(javax.swing.grouplayout.alignment.leading).addgroup(javax.swing.grouplayout.alignment.trailing, layout.createsequentialgroup().addcontainergap(javax.swing.grouplayout.default_size, short.max_value).addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.leading).addgroup(javax.swing.grouplayout.alignment.trailing, layout.createsequentialgroup().addcomponent(calllist_button).addgap(41, 41, 41).addcomponent(putamc_button).addgap(28, 28, 28).addcomponent(generatereport_button).addgap(74, 74, 74)).addgroup(javax.swing.grouplayout.alignment.trailing, layout.createsequentialgroup().addcomponent(solaris_logo).addgap(132, 132, 132)))).addgroup(layout.createsequentialgroup().addgap(20, 20, 20).addcomponent(addnewsales_button).addgap(44, 44, 44).addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.leading).addgroup(layout.createsequentialgroup().addcomponent(support_label, javax.swing.grouplayout.preferred_size, 130, javax.swing.grouplayout.preferred_size).addcontainergap()).addgroup(layout.createsequentialgroup().addcomponent(serialnocheck_button).addpreferredgap(javax.swing.layoutstyle.componentplacement.related, 43, short.max_value).addcomponent(newcomplaint_button).addgap(23, 23, 23)))));     layout.setverticalgroup(               layout.createparallelgroup(javax.swing.grouplayout.alignment.leading).addgroup(layout.createsequentialgroup().addgap(32, 32, 32).addcomponent(solaris_logo, javax.swing.grouplayout.preferred_size, 47, javax.swing.grouplayout.preferred_size).addpreferredgap(javax.swing.layoutstyle.componentplacement.related).addcomponent(support_label, javax.swing.grouplayout.preferred_size, 35, javax.swing.grouplayout.preferred_size).addpreferredgap(javax.swing.layoutstyle.componentplacement.related, 72, short.max_value).addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.baseline).addcomponent(addnewsales_button).addcomponent(serialnocheck_button).addcomponent(newcomplaint_button)).addgap(28, 28, 28).addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.baseline).addcomponent(calllist_button).addcomponent(generatereport_button).addcomponent(putamc_button)).addgap(34, 34, 34)));  }   private void putamc_buttonactionperformed(java.awt.event.actionevent evt) {     // todo add handling code here:      amc();     mainframe.add(amc);     mainframe.remove(firstpane);     mainframe.validate();     mainframe.repaint();     mainframe.pack(); }  private void amc() {      amc=new jpanel();     custname_label = new javax.swing.jlabel();     custname_txtbox = new javax.swing.jtextfield();     amc_search_button = new javax.swing.jbutton();      amc.setborder(javax.swing.borderfactory.createtitledborder(null, "amc sign up", javax.swing.border.titledborder.default_justification, javax.swing.border.titledborder.default_position, null, new java.awt.color(0, 0, 0)));      custname_label.settext("enter customer name");      amc_search_button.settext("search");     amc_search_button.addactionlistener(new java.awt.event.actionlistener() {         public void actionperformed(java.awt.event.actionevent evt) {             amc_search_buttonactionperformed(evt);         }     });      javax.swing.grouplayout layout = new javax.swing.grouplayout(amc);     amc.setlayout(layout);     layout.sethorizontalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addcomponent(custname_label)             .addgap(18, 18, 18)             .addcomponent(custname_txtbox, javax.swing.grouplayout.preferred_size, 173, javax.swing.grouplayout.preferred_size)             .addgap(0, 46, short.max_value))         .addgroup(layout.createsequentialgroup()             .addgap(116, 116, 116)             .addcomponent(amc_search_button)             .addcontainergap())     );     layout.setverticalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addgap(46, 46, 46)             .addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.baseline)                 .addcomponent(custname_label)                 .addcomponent(custname_txtbox, javax.swing.grouplayout.preferred_size, javax.swing.grouplayout.default_size, javax.swing.grouplayout.preferred_size))             .addgap(51, 51, 51)             .addcomponent(amc_search_button)             .addcontainergap(136, short.max_value))     ); }  private void amc_search_buttonactionperformed(java.awt.event.actionevent evt) {     // todo add handling code here:     cust_name=custname_txtbox.gettext().trim();         try {             preparedstatement pre = con.preparestatement("select *   productinformation customername='"+cust_name+"'");              vector<vector<string>> historyvector = new vector<vector<string>>();              rs = pre.executequery();  while(rs.next()) {  vector<string> history = new vector<string>();  serial_no=rs.getstring("serialnumber");  system.out.println("here");//empid  history.add(serial_no);  history.add(rs.getstring("model"));  history.add(rs.getstring("invoicenumber"));  history.add(rs.getstring("location"));         historyvector.add(history);    }              data=historyvector;              header = new vector<string>();     header.add("serial no");      header.add("model");     header.add("invoice no");      header.add("location");     header.add("asc");     header.add("amc");            amcascresult();     mainframe.add(amcascresult);     mainframe.remove(amc);     mainframe.validate();     mainframe.repaint();     mainframe.pack();         }         catch(exception e){             system.err.println(e);         }   }  private void amcascresult() {     amcascresult=new jpanel();     custname_label = new javax.swing.jlabel();     custname_var_label = new javax.swing.jlabel();     location_label = new javax.swing.jlabel();     custlocation_var_label = new javax.swing.jlabel();     jscrollpane1 = new javax.swing.jscrollpane();     amcasc_table = new javax.swing.jtable();     putamcasc_button = new javax.swing.jbutton();      amcascresult.setborder(javax.swing.borderfactory.createtitledborder("put amc"));      custname_label.settext("customer name :");      custname_var_label.settext(cust_name);      location_label.settext("location :");      custlocation_var_label.settext("<location>");      amcasc_table.setmodel(new javax.swing.table.defaulttablemodel(         data,header     ) {         boolean[] canedit = new boolean [] {             false, false, false, true, true         };          private static final long serialversionuid = 1l;          /*@override         public class getcolumnclass(int column) {         return getvalueat(0, column).getclass();         }*/         @override         public class getcolumnclass(int column) {             switch (column) {                 case 0:                     return string.class;                 case 1:                     return string.class;                 case 2:                     return string.class;                 case 3:                     return string.class;                 default:                     return boolean.class;             }         }          public boolean iscelleditable(int rowindex, int columnindex) {             return canedit [columnindex];         }     });     jscrollpane1.setviewportview(amcasc_table);      putamcasc_button.settext("put amc/asc");     putamcasc_button.addactionlistener(new java.awt.event.actionlistener() {         public void actionperformed(java.awt.event.actionevent evt) {             putamcasc_buttonactionperformed(evt);         }     });      javax.swing.grouplayout layout = new javax.swing.grouplayout(amcascresult);     amcascresult.setlayout(layout);     layout.sethorizontalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addcontainergap()             .addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.trailing)                 .addcomponent(putamcasc_button)                 .addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)                     .addgroup(layout.createsequentialgroup()                         .addcomponent(custname_label)                         .addpreferredgap(javax.swing.layoutstyle.componentplacement.unrelated)                         .addcomponent(custname_var_label)                         .addgap(18, 18, 18)                         .addcomponent(location_label)                         .addgap(18, 18, 18)                         .addcomponent(custlocation_var_label))                     .addcomponent(jscrollpane1, javax.swing.grouplayout.preferred_size, 375, javax.swing.grouplayout.preferred_size)))             .addcontainergap(javax.swing.grouplayout.default_size, short.max_value))     );     layout.setverticalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addcontainergap()             .addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.baseline)                 .addcomponent(custname_label)                 .addcomponent(custname_var_label)                 .addcomponent(location_label)                 .addcomponent(custlocation_var_label))             .addpreferredgap(javax.swing.layoutstyle.componentplacement.unrelated)             .addcomponent(jscrollpane1, javax.swing.grouplayout.preferred_size, 213, javax.swing.grouplayout.preferred_size)             .addpreferredgap(javax.swing.layoutstyle.componentplacement.related, 10, short.max_value)             .addcomponent(putamcasc_button))     ); }  private void putamcasc_buttonactionperformed(java.awt.event.actionevent evt) {     // todo add handling code here:     (int = 0; <amcasc_table.getrowcount(); i++) {  boolean ischecked = (boolean) amcasc_table.getvalueat(i, 4);   if (ischecked) {     //get values of columns need.   string value = (string) amcasc_table.getvalueat(i, 0);   system.out.println(value);    } }     amcascconfirm();     mainframe.add(amcascconfirm);     mainframe.remove(amcascresult);     mainframe.validate();     mainframe.repaint();     mainframe.pack(); }   private void amcascconfirm() {     amcascconfirm=new jpanel();      confirm_label = new javax.swing.jlabel();     finish_button = new javax.swing.jbutton();      amcascconfirm.setborder(javax.swing.borderfactory.createtitledborder("confirmation   of amc/asc"));      confirm_label.settext("amc/asc has been availed machines selected");      finish_button.settext("finish");     finish_button.addactionlistener(new java.awt.event.actionlistener() {         public void actionperformed(java.awt.event.actionevent evt) {             finish_button1actionperformed(evt);         }     });      javax.swing.grouplayout layout = new javax.swing.grouplayout(amcascconfirm);     amcascconfirm.setlayout(layout);     layout.sethorizontalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addgroup(layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)                 .addgroup(layout.createsequentialgroup()                     .addgap(73, 73, 73)                     .addcomponent(confirm_label)                     .addgap(0, 95, short.max_value))                 .addgroup(javax.swing.grouplayout.alignment.trailing,   layout.createsequentialgroup()                     .addcontainergap(javax.swing.grouplayout.default_size, short.max_value)                     .addcomponent(finish_button)))             .addcontainergap())     );     layout.setverticalgroup(         layout.createparallelgroup(javax.swing.grouplayout.alignment.leading)         .addgroup(layout.createsequentialgroup()             .addgap(59, 59, 59)             .addcomponent(confirm_label)             .addpreferredgap(javax.swing.layoutstyle.componentplacement.related, 169, short.max_value)             .addcomponent(finish_button)             .addcontainergap())     ); }   private void finish_button1actionperformed(java.awt.event.actionevent evt) {     // todo add handling code here:       mainframe.add(firstpane);      mainframe.remove(amcascconfirm);      mainframe.validate();      mainframe.repaint();      mainframe.pack(); }  private javax.swing.jlabel confirm_label; private javax.swing.jbutton finish_button; private javax.swing.jtable amcasc_table; private javax.swing.jlabel custlocation_var_label; private javax.swing.jlabel custname_label; private javax.swing.jlabel custname_var_label; private javax.swing.jscrollpane jscrollpane1; private javax.swing.jlabel location_label; private javax.swing.jbutton putamcasc_button;  private javax.swing.jbutton amc_search_button; private javax.swing.jtextfield custname_txtbox;  private javax.swing.jlabel support_label; private javax.swing.jbutton addnewsales_button; private javax.swing.jbutton calllist_button; private javax.swing.jbutton generatereport_button; private javax.swing.jbutton newcomplaint_button; private javax.swing.jbutton putamc_button; private javax.swing.jbutton serialnocheck_button; private javax.swing.jlabel solaris_logo;  } 

among 700+ lines of incomplete example, several issues stand out:

• the word sometimes suggests incorrect synchronization; verify swing gui objects constructed , manipulated only on event dispatch thread.

• ensure tablemodel returns boolean.class getcolumnclass() checkbox column, rather merely default; complete examples using defaulttablemodel may seen here , here.

• don't replace components, e.g. amc in first fragment , amcascconfirm in magnum opus; update corresponding model of contained component.

• verify correct query results independently of program; select * particularly troublesome if schema mutates.