I'd like to get a value from a table. If the column does not contain any value, then I am going to insert one.

If there is a value, I want to notify the user that a value was inserted already. When my table does not contain anything it shows an error as Java Null Pointer Exception. I want to get a null value from my table. Please help.

                   String qu="select * from userinfos";
                   c=db.rawQuery(qu,null);

                   int count = c.getCount();

                   String[] values = new String[count + 1];
                   int i = 0;
                   for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
                       values[i] = c.getString(c.getColumnIndex("mail"));
                       Toast.makeText(FiveActivity.this, values[i],Toast.LENGTH_LONG).show();
                       i++;
                    }  

                   i=0;
                   if(values[i].equals(null))
                   {
                   String    Query =    "insert into userinfos (mail,pass) values ('"+ mailuser+ "','" + password + "')";
                   db.execSQL(Query);
                   Toast.makeText(FiveActivity.this,"Values Inserted",Toast.LENGTH_LONG).show();
                   }
                   else
                   {
                       for(int j=0;j<3;j++)
                       Toast.makeText(FiveActivity.this,"Already one Email-Id:"+ values[i]+" "+"you given. if you want to insert new mail and password then go to Delete app",Toast.LENGTH_LONG).show();

                   }

You just need to check your count value like below:

 c=db.rawQuery(qu,null);

 int count = c.getCount();

 if(count==0)
{
////// No data found
}
 else
{
 /////data available
}

getCount ()

Returns the numbers of rows in the cursor

http://developer.android.com/reference/android/database/Cursor.html#getCount

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