# getting preferences from a specified file
SharedPreferences settings = getSharedPreferences("Test", Context.MODE_PRIVATE);

SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(getActivity());
String url = settings.getString("url", "n/a");

Editor edit = preferences.edit();
edit.putString("username", "new_value_for_user");
edit.apply();

SharedPreferences prefs = 
    PreferenceManager.getDefaultSharedPreferences(this);

// Instance field for listener
listener = new SharedPreferences.OnSharedPreferenceChangeListener() {
  public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
    // Your Implementation
  }
};

prefs.registerOnSharedPreferenceChangeListener(listener);

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >

    <EditTextPreference
        android:key="url"
        android:title="Rss feed URL" 
        android:inputType="textUri"/>
    <CheckBoxPreference android:title="Aktiv" android:key="active"/>

</PreferenceScreen>

package com.example.android.rssreader;

import android.os.Bundle;
import android.preference.PreferenceFragment;

public class SettingsFragment extends PreferenceFragment  {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.mypreferences);
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // more code...
    case R.id.action_settings:
        // Launch settings activity
        if (getResources().getBoolean(R.bool.twoPaneMode)) {
            getFragmentManager().beginTransaction().replace(R.id.detailFragment, new
                    SettingsFragment()).commit();
        } else {
            getFragmentManager().beginTransaction().addToBackStack(null).replace(R.id
                     .fragment_container, new SettingsFragment()).commit();
        }
        return true;
        // more code...
    }
    // more code...
}

// if you use this in a service or activity you can use this
// if you use this in a fragment use getActivity() or getContent() as parameter
SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(this);
String url = settings.getString("url", "https://www.vogella.com/article.rss");

package com.example.android.rssreader;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.EditTextPreference;
import android.preference.Preference;
import android.preference.PreferenceCategory;
import android.preference.PreferenceFragment;

public class SettingsFragment extends PreferenceFragment  implements SharedPreferences.OnSharedPreferenceChangeListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.mypreferences);
        // show the current value in the settings screen
        for (int i = 0; i < getPreferenceScreen().getPreferenceCount(); i++) {
            initSummary(getPreferenceScreen().getPreference(i));
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        getPreferenceScreen().getSharedPreferences()
                .registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onPause() {
        super.onPause();
        getPreferenceScreen().getSharedPreferences()
                .unregisterOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
                                          String key) {
        updatePreferences(findPreference(key));
    }

    private void initSummary(Preference p) {
        if (p instanceof PreferenceCategory) {
            PreferenceCategory cat = (PreferenceCategory) p;
            for (int i = 0; i < cat.getPreferenceCount(); i++) {
                initSummary(cat.getPreference(i));
            }
        } else {
            updatePreferences(p);
        }
    }

    private void updatePreferences(Preference p) {
        if (p instanceof EditTextPreference) {
            EditTextPreference editTextPref = (EditTextPreference) p;
            p.setSummary(editTextPref.getText());
        }
    }
}

public class Util {
    public static void writeConfiguration(Context ctx, String s ) {
        try (FileOutputStream openFileOutput =
             ctx.openFileOutput( "config.txt", Context.MODE_PRIVATE);) {

            openFileOutput.write(s.getBytes());
        } catch (Exception e) {
            // not handled
        }
    }
}

public void readFileFromInternalStorage(String fileName) {
    String eol = System.getProperty("line.separator");
    try (BufferedReader input = new BufferedReader(new InputStreamReader(
        openFileInput(fileName))); ){
      String line;
      StringBuffer buffer = new StringBuffer();
      while ((line = input.readLine()) != null) {
        buffer.append(line + eol);
      }
    } catch (Exception e) {
        // we do not care
    }
}

Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)

private void readFileFromSDCard() {
    File directory = Environment.getExternalStorageDirectory();
    // assumes that a file article.rss is available on the SD card
    File file = new File(directory + "/article.rss");
    if (!file.exists()) {
        throw new RuntimeException("File not found");
    }
    Log.e("Testing", "Starting to read");
    BufferedReader reader = null;
    try {
        reader = new BufferedReader(new FileReader(file));
        StringBuilder builder = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            builder.append(line);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}