android default values for shared preferences

I am trying to understand the SharedPreferences of Android. I am a beginner and don't know a lot about it.

I have this class I implemented for my app Preferences

public class Preferences {
    public static final String MY_PREF = "MyPreferences";

    private SharedPreferences sharedPreferences;
    private Editor editor;

    public Preferences(Context context) {
        this.sharedPreferences = context.getSharedPreferences(MY_PREF, 0);
        this.editor = this.sharedPreferences.edit();
    }

    public void set(String key, String value) {
        this.editor.putString(key, value);
        this.editor.commit();
    }

    public String get(String key) {
        return this.sharedPreferences.getString(key, null);
    }

    public void clear(String key) {
        this.editor.remove(key);
        this.editor.commit();
    }

    public void clear() {
        this.editor.clear();
        this.editor.commit();
    }
}

The thing is that I would like to set default preferences. They would be set when the app is installed and could be modified after by the application and stay persistent. I heard about a preferences.xml but I don't understand the process.

Could someone help me?

Thanks for you time