Androidでの画面遷移

以下のようにsaveButtonを押すとSettingFragmentに遷移（それがやりたいこと）するようなコードを書きました。

Java
1 saveButton.setOnClickListener(new View.OnClickListener() {
2            @Override
3            public void onClick(View v) {
4                SavePreference savePreference = new SavePreference();
5                String aToken = savePreference.load_aToken(getApplicationContext());
6                savePreference.save_aToken(ProfileActivity.this, aToken);
7                UserInfoApi userInfoApi = ServiceGenerator.createService(UserInfoApi.class, aToken);
8                String sexData = sexEditAdapter.getItem(sexEdit.getSelectedItemPosition()).first;
9                String areaData = areaSpinnerAdapter.getItem(areaSpinner.getSelectedItemPosition()).first;
10                String birthData = (birthYear.getSelectedItemPosition() + 1900) + "-" + (birthMonth.getSelectedItemPosition() + 1) + "-" + (birthDay.getSelectedItemPosition() + 1);
11                UserInfoApi api = ServiceGenerator.createService(UserInfoApi.class, aToken);
12                email = RequestBody.create(MediaType.parse("multipart/form-data"), String.valueOf(mailEdit.getText()));
13                sex = RequestBody.create(MediaType.parse("multipart/form-data"), sexData);
14                birthday = RequestBody.create(MediaType.parse("multipart/form-data"), birthData);
15                username = RequestBody.create(MediaType.parse("multipart/form-data"), String.valueOf(usernametext.getText()));
16                area = RequestBody.create(MediaType.parse("multipart/form-data"), areaData);
17                bio = RequestBody.create(MediaType.parse("multipart/form-data"), String.valueOf(introductiontext.getText()));
18call.enqueue(new Callback<UserInfo>() {
19                    @Override
20                    public void onResponse(Call<UserInfo> call, Response<UserInfo> response) {
21
22                        Intent nextActivity = new Intent(getActivity(), SettingFragment.class);
23                        startActivity(nextActivity);
24
25                    }

しかし、

Java
1Intent nextActivity = new Intent(getActivity(), SettingFragment.class);
2

のところのgetActivity()でCannot resolve methodとでました。

Java
1import android.app.Activity;
2import android.content.Intent;
3import android.os.Bundle;
4import android.view.View;
5import android.widget.Button;
6 
7public class MainActivity extends Activity {
8 
9	@Override
10	protected void onCreate(Bundle savedInstanceState) {
11		super.onCreate(savedInstanceState);
12		setContentView(R.layout.activity_main);
13 
14		Button sendButton = (Button) findViewById(R.id.send_button);
15		sendButton.setOnClickListener(new View.OnClickListener() {
16			@Override
17			public void onClick(View v) {
18				Intent intent = new Intent(getApplication(), SubActivity.class);
19				startActivity(intent);
20			}
21		});
22	}
23}

と描かれているWEBを参考にして作りました。こちらではgetApplication()は定義されていないようです。
自分のコードでどのように定義すべきでしょうか？

クラスの宣言部分には

Java
1public class ProfileActivity extends Activity {
2
3
4    private Bitmap bitmap;
5    private byte[] bytes;
6    private Uri bitmapUri;
7    private RequestBody icon_img;
8    private static final int REQUEST_CODE_CAMERA = 1;
9    private static final int REQUEST_CODE_GALLERY = 2;
10    private EditText mailEdit;
11    private EditText nicknametex;
12    private EditText usernametext;
13    private EditText introductiontext;
14    private Spinner areaSpinner;
15    private Spinner sexEdit;
16    private Spinner birthYear;
17    private Spinner birthMonth;
18    private Spinner birthDay;
19    private Button saveButton;
20    private ArrayAdapter parentSpinnerAdapter, childSpinnerAdapter;
21    private Spinner parentSpinner, childSpinner;
22    private ImageButton icon;
23    private RequestBody email;
24    private RequestBody sex;
25    private RequestBody birthday;
26    private RequestBody username;
27    private RequestBody area;
28    private RequestBody bio;
29    private UserInfoApi userInfoApi;
30    private TextView privacy_link, terms_link, forgotten_link, user_regist;
31    private static final int USER_REGIST = 1;
32    private com.google.firebase.analytics.FirebaseAnalytics FirebaseAnalytics;
33    /**
34     * ATTENTION: This was auto-generated to implement the App Indexing API.
35     * See https://g.co/AppIndexing/AndroidStudio for more information.
36     */
37    private GoogleApiClient client;
38    private Button SaveButton;
39    private KeyValuePairAdapter sexEditAdapter;
40    private KeyValuePairAdapter areaSpinnerAdapter;
41
42