public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    try{
        UserAgent userAgent = new UserAgent();
        userAgent.visit("http://jaunt-api.com/examples/signup.htm");
        ///Document doc = userAgent.doc;

        ///doc.fillout("E-mail:", "tom@mail.com");  //fill out the (textfield) component labelled "E-mail:"
        ///doc.choose("Account Type:", "advanced"); //choose "advanced" from the menu labelled "Account Type:"
        ///doc.fillout("Comments:", "no comment");  //fill out the (textarea) component labelled "Comments:"
        ////doc.choose(Label.RIGHT, "No thanks");    //choose the (radiobutton) component right-labelled "No thanks"
        ////doc.submit("create trial account");      //press the submit button labelled 'create trial account'
        ///System.out.println(userAgent.getLocation());  //print the current location (url)
    }
    catch(JauntException e){
        System.out.println(e);
    }

}

java.lang.NullPointerException: Attempt to invoke interface method 'void com.android.okhttp.internal.http.Transport.writeRequestHeaders(com.android.okhttp.Request)' on a null object reference

try{
  UserAgent userAgent = new UserAgent();
  userAgent.visit("http://jaunt-api.com/examples/signup.htm");

  userAgent.doc.apply(     //fill-out the form by applying a sequence of inputs
    "tom@mail.com",        //string input is applied to textfield
    "(advanced)",          //bracketed string (regular expression) selects a menu item
    "no comment",          //string input is applied to textarea
    1                      //integer specifies index of radiobutton choice
  );
  userAgent.doc.submit("create trial account"); //press the submit button labelled 'create trial account'
  System.out.println(userAgent.getLocation());  //print the current location (url)
}
catch(JauntException e){
  System.out.println(e);
}

<manifest xlmns:android...>
 ...
 <uses-permission android:name="android.permission.INTERNET" />
 <application ...
</manifest>

private class OkHttpHandler extends AsyncTask<String, Void, byte[]> {



            @Override
            protected byte[] doInBackground(String... params) {

            UserAgent userAgent = new UserAgent();
            userAgent.visit("http://jaunt-api.com/examples/signup.htm");

                return null;
            }

            @Override
            protected void onPostExecute(byte[] bytes) {
                super.onPostExecute(bytes);

    try{

      Form form = userAgent.doc.getForm(0);       //get the document's first Form
      form.setTextField("email", "tom@mail.com"); //or form.set("email", "tom@mail.com");
      form.setPassword("pw", "secret");           //or form.set("pw", "secret");
      form.setCheckBox("remember", true);         //or form.set("remember", "on");
      form.setSelect("account", "advanced");      //or form.set("account", "advanced");
      form.setTextArea("comment", "no comment");  //or form.set("comment", "no comment");
      form.setRadio("inform", "no");              //or form.set("inform", "no");
      form.submit("create trial account");        //click the submit button labelled 'create trial account'
      System.out.println(userAgent.getLocation());//print the current location (url)
    }
    catch(JauntException e){
      System.err.println(e);
    }

        }
 }

new OkHttpHandler().execute();