在没有任何上下文的情况下获取Android的系统首选项

import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {

    SharedPreferences sharedPreferences;
    Editor editor;

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

        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        editor = sharedPreferences.edit();

        Button btnSave = findViewById(R.id.btn_save);
        Button btnLoad = findViewById(R.id.btn_load);
        EditText etUsername = findViewById(R.id.et_username);
        EditText etPassword = findViewById(R.id.et_password);

        // Save user preferences
        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                editor.putString("username", etUsername.getText().toString());
                editor.putString("password", etPassword.getText().toString());
                editor.apply();
            }
        });

        // Load user preferences
        btnLoad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = sharedPreferences.getString("username", "");
                String password = sharedPreferences.getString("password", "");
                etUsername.setText(username);
                etPassword.setText(password);
            }
        });
    }
}