title: problem with sending multiple data between activities android
body: <p>i want to send multiple data from activity WelcomeScreen to OpenBook 
  here is my code  </p>
  
  <p><strong>Sending</strong></p>
  
  <pre><code>
  String a="pg558.sqlite";
          String b="pg558";
          Intent intent = new Intent(getApplicationContext(), OpenBook.class);
          intent.putExtra("db_name",a);
          intent.putExtra("book_name",b);
          intent.putExtra("chapter_number",3);
          intent.putExtra("page_number",1);
          startActivity(intent);
  </code></pre>
  
  <p><strong>Recieving</strong></p>
  
  <pre><code>
  Bundle b = getIntent().getExtras();
          DB_NAME= b.getString("db_name");
          BOOK_NAME= b.getString("book_name");
          CHAPTER_NUMBER= b.getInt("chapter_number",1);
          PAGE_NUMBER= b.getInt("page_number",1);
  </code></pre>
  
  <p>i'm getting runtime error   </p>
  
  <p><code>
  03-21 16:29:34.989: ERROR/AndroidRuntime(10651): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mireader/com.mireader.OpenBook}: java.lang.NullPointerException
  </code></p>