android - displaying contents of an sqlite database -

i have update page allows inserting, updating , displaying contents of database. xml layout file looks this:

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bckg1" android:gravity="top" android:orientation="vertical" >  <textview     android:id="@+id/gotomenu"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentbottom="true"     android:layout_alignparentright="true"     android:layout_marginbottom="46dp"     android:layout_marginright="18dp"     android:text="go main menu"     android:textcolor="#221778"     android:textsize="15sp" />  <edittext     android:id="@+id/entryforroll"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignbottom="@+id/rollno"     android:layout_alignparentright="true"     android:layout_torightof="@+id/attendancepercent"     android:ems="10"     android:inputtype="textpersonname"     android:hint="enter roll number" >      <requestfocus /> </edittext>  <textview     android:id="@+id/rollno"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentleft="true"     android:layout_alignparenttop="true"     android:layout_margintop="58dp"     android:text="roll number:"     android:textappearance="?android:attr/textappearancelarge"     android:textcolor="#221778"     android:textstyle="bold" />  <button     android:id="@+id/show"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_above="@+id/gotomenu"     android:layout_toleftof="@+id/gotomenu"     android:text="show"     android:textcolor="#221778"     android:textstyle="bold"      android:onclick="getall"     />  <button     android:id="@+id/insert"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_above="@+id/show"     android:layout_alignleft="@+id/name"     android:layout_marginbottom="36dp"     android:text="insert"     android:textcolor="#221778"     android:textstyle="bold"      />  <button     android:id="@+id/update"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignbaseline="@+id/insert"     android:layout_alignbottom="@+id/insert"     android:layout_alignright="@+id/gotomenu"     android:text="update"     android:textcolor="#221778"     android:textstyle="bold"      />  <textview     android:id="@+id/attendancepercent"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_above="@+id/insert"     android:layout_alignparentleft="true"     android:layout_marginbottom="23dp"     android:text="attendance %:"     android:textappearance="?android:attr/textappearancelarge"     android:textcolor="#221778"     android:textstyle="bold" />  <textview     android:id="@+id/name"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentleft="true"     android:layout_below="@+id/rollno"     android:layout_margintop="24dp"     android:text="name:"     android:textappearance="?android:attr/textappearancelarge"     android:textcolor="#221778"     android:textsize="22sp"     android:textstyle="bold" />  <edittext     android:id="@+id/entryforname"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignbottom="@+id/name"     android:layout_alignleft="@+id/show"     android:ems="10"     android:inputtype="textpersonname"     android:hint="enter name" />  <edittext     android:id="@+id/entryforpercentage"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignbottom="@+id/attendancepercent"     android:layout_torightof="@+id/show"     android:ems="10"     android:hint="enter %" /> 

now 3 buttons perform actions of insert, update , display.the java code given below :

    package com.vidhi.grietportal;      import android.app.activity;     import android.content.intent;     import android.database.cursor;     import android.database.sqlite.sqlitedatabase;     import android.graphics.color;     import android.graphics.typeface;     import android.os.bundle;     import android.view.view;     import android.view.view.onclicklistener;     import android.widget.button;     import android.widget.edittext;     import android.widget.tablelayout;     import android.widget.tablerow;     import android.widget.textview;      public class update extends activity {       button b1,b2,b3;     edittext e1,e2,e3;     attendancedatabaseadapter adb;     sqlitedatabase db;     databasehelper dbh;     textview tv1;      @override     protected void oncreate(bundle savedinstancestate) {     // todo auto-generated method stub     super.oncreate(savedinstancestate);     setcontentview(r.layout.update);       adb= new attendancedatabaseadapter(this);     adb=adb.open();      b1=(button)findviewbyid(r.id.insert);     b2=(button)findviewbyid(r.id.update);     b3=(button)findviewbyid(r.id.show);      e1=(edittext)findviewbyid(r.id.entryforroll);     e2=(edittext)findviewbyid(r.id.entryforname);     e3=(edittext)findviewbyid(r.id.entryforpercentage);      final string roll=e1.gettext().tostring();     final string name=e2.gettext().tostring();     final string percent=e3.gettext().tostring();       b1.setonclicklistener(new onclicklistener() {          @override         public void onclick(view arg0) {             // todo auto-generated method stub                adb.insertentry(roll,name,percent);          }     });      b2.setonclicklistener(new onclicklistener() {          @override         public void onclick(view arg0) {             // todo auto-generated method stub             adb.updateentry(roll,name,percent);          }     });     b3.setonclicklistener(new onclicklistener() {  @override public void onclick(view v) {     // todo auto-generated method stub     intent ine=new intent(v.getcontext(),displayatt.class);     startactivityforresult(ine, 0); }     });     }     } 

the adapter class follows:

package com.vidhi.grietportal; import android.content.contentvalues; import android.content.context; import android.database.cursor; import android.database.sqlexception; import android.database.sqlite.sqlitedatabase;  public class attendancedatabaseadapter  {  public final string database_name="griet.db"; static final int database_version=2; static final int name_column=1; public sqlitedatabase db; private final context context; private databasehelper dbhelper; public attendancedatabaseadapter(context _context) {      context=_context;      dbhelper=new databasehelper(context, database_name, null, database_version); } public attendancedatabaseadapter open() throws sqlexception {     db=dbhelper.getwritabledatabase();     return this; } public void close() {      db.close(); } public sqlitedatabase getdatabaseinstance() {     return db; } public void insertentry(string roll,string name,string percent) {     contentvalues newcontent=new contentvalues();     newcontent.put("rollno",roll);     newcontent.put("stuname", name);     newcontent.put("percentage",percent);      db.insert("attendance",null, newcontent);   }  public void updateentry(string roll,string name,string percent) {     contentvalues newupdate=new contentvalues();     newupdate.put("rollno", roll);     newupdate.put("stuname",name);     newupdate.put("percentage", percent);      string where="rollno=?";     db.update("attendance", newupdate, where, new string[] {roll});  }  public cursor getall()  {      return db.query("attendance", new string[] {"rollno","stuname",             "percentage"}, null, null, null, null, null); }   } 

the databasehelper class follows:

package com.vidhi.grietportal; import android.content.context; import android.database.sqlite.sqlitedatabase; import android.database.sqlite.sqliteopenhelper; import android.database.sqlite.sqlitedatabase.cursorfactory;  public class databasehelper extends sqliteopenhelper {  private static final string table1 = "login"; private static final string table2 = "attendance"; private static final string column_id = "id"; private static final string column_title1 = "username"; private static final string column_title2 = "password"; private static final string column_id1 = "id1"; private static final string column_title3 = "rollno"; private static final string column_title4 = "stuname"; private static final string column_title5 = "percentage";   public static final string table1_creation = "create table " + table1 + " (" + column_id + "     integer primary key autoincrement, " + column_title1 + " text,"+ column_title2 +" text"+")"; public static final string table2_creation = "create table " + table2 + " (" + column_id1 + " integer primary key autoincrement, " + column_title3 + " text,"+ column_title4 +" text,"+   column_title5 +" text"+")";   public databasehelper(context context, string name, cursorfactory factory, int version) {     super(context, name, factory, version); }  @override public void oncreate(sqlitedatabase db) {     db.execsql(table1_creation);     db.execsql(table2_creation);  }  @override public void onupgrade(sqlitedatabase db, int paramint1, int paramint2) {     db.execsql("drop table " + table1_creation + ";");     db.execsql("drop table " + table2_creation + ";");      oncreate(db);  } } 

the displayatt class given follows:

package com.vidhi.grietportal;  import android.app.activity; import android.database.cursor; import android.os.bundle; import android.widget.textview;   public class displayatt extends activity {  attendancedatabaseadapter adb; databasehelper dbh1; textview tv1=(textview)findviewbyid(r.id.textview1999);   @override protected void oncreate(bundle savedinstancestate) {     // todo auto-generated method stub     super.oncreate(savedinstancestate);     setcontentview(r.layout.displayatt);      adb.open();     //db.fetchallnotes();     cursor c = adb.getall();     int i=1;     if (c.movetofirst())   {                 {             displaycontact(c,i++);         } while (c.movetonext());     }     c.close();     adb.close(); }   public void displaycontact(cursor c,int row )   {                   string name11 = c.getstring(1) + c.getstring(2) + c.getstring(3);                 tv1.settext(name11 );    }    } 

we wish display contents of attendance table using displayatt class. code giving me null pointer exception. please !

i don´t know if all, haven´t initialized attendancedatabaseadapter. must in oncreate()

   adb = new attendancedatabaseadapter(this); 

before call

   adb.open();