title: Getting Null Pointer Exception while saving a checkbox value into database
body: <p>i want to add checkbox value into database,but it is showing error in the logcat,i had stored my value in variable "ta" and i have toasted it,then it is working,and when i am inserting that value into database it is showing error </p>
  
  <pre><code>package com.example.hhh;
  
  import android.os.Build;
  import android.os.Bundle;
  import android.annotation.SuppressLint;
  import android.annotation.TargetApi;
  import android.app.ActionBar;
  import android.app.ActionBar.Tab;
  import android.app.ActionBar.TabListener;
  import android.app.Activity;
  import android.view.Menu;
  import android.view.View;
  import android.view.View.OnClickListener;
  import android.widget.Button;
  import android.widget.CheckBox;
  import android.widget.Toast;
  
  
  public class MainActivity extends Activity implements OnClickListener {
  
  CheckBox ct1,ct2,ct3,ct4;
  protected DatabaseAdapter helper;
  String ta;
  
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      helper=new DatabaseAdapter(this);
      helper.open();
  
          ct1=(CheckBox)findViewById(R.id.checkBox1);
          ct2=(CheckBox)findViewById(R.id.checkBox2);
          ct3=(CheckBox)findViewById(R.id.checkBox3);
          ct4=(CheckBox)findViewById(R.id.checkBox4);
  
          ct1.setOnClickListener(this);
          ct2.setOnClickListener(this);
          ct3.setOnClickListener(this);
          ct4.setOnClickListener(this);
  
  
  
  }
  
  
  
  
  @Override
  public void onClick(View v) {
      // TODO Auto-generated method stub
      CheckBox ct=(CheckBox)v;
      if(ct.isChecked())
      {
           ta=ct.getText().toString();
           helper.Add(ta);
              Toast.makeText(MainActivity.this, ""+ta,
  
      Toast.LENGTH_SHORT).show();
              helper.close();
  
  
      }
  }
  
  
  
  
  
   }
  </code></pre>
  
  <p>abd database class is
      package com.example.hhh;</p>
  
  <pre><code>import android.content.ContentValues;
  import android.content.Context;
  import android.database.sqlite.SQLiteDatabase;
  import android.database.sqlite.SQLiteDatabase.CursorFactory;
  import android.database.sqlite.SQLiteOpenHelper;
  import android.util.Log;
  
  public class DatabaseAdapter {
  
  SQLiteDatabase db;
  DatabaseHelper helper;
  public static final String DATABASE="Hotel";
  public static final int VERSION=2;
  public static final String query="create table hhh(id integer primary key,room text
      not null)";
  private Context ctx;
  
  public DatabaseAdapter(Context ctx) {
      super();
      this.ctx=ctx;
  }
  
  
  
  
  
  public class DatabaseHelper extends SQLiteOpenHelper
  {
  
      public DatabaseHelper(Context context
      ) {
          super(context, DATABASE, null, VERSION);
          // TODO Auto-generated constructor stub
      }
  
      @Override
      public void onCreate(SQLiteDatabase db) {
          // TODO Auto-generated method stub
          db.execSQL(query);
  
      }
  
      @Override
      public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
          // TODO Auto-generated method stub
  
      }
  
  }
  
  
  
  
  
  public DatabaseAdapter open() {
      helper=new DatabaseHelper(ctx);
      db=helper.getWritableDatabase();
      return this;
      // TODO Auto-generated method stub
  
  }
  
  
  
  
  
  public void close() {
      // TODO Auto-generated method stub
      helper.close();
  }
  
  public long Add(String ta)
  {
      ContentValues vals=new ContentValues();
      vals.put("room", ta);
      long a=db.insert("Hotel", null, vals);
      return a;
  
  }
  
  
  
    }
  </code></pre>
  
  <p>and i sloved it by intializing "db" in open() method.</p>