Activity以外から更新とSharedPreferencesの使い方

TextChange.java

import android.content.Context;
import android.content.SharedPreferences;
import android.widget.TextView;

import static android.content.Context.MODE_PRIVATE;

public class TextChange {

    private Context appContext;

    public TextChange(Context context) {
        appContext = context;
    }

    public void textChange() {
        TextView textView1 = (TextView)((MainActivity)appContext).findViewById(R.id.textView1);
        textView1.setText("アイウエオ");
        SharedPreferences pref = appContext.getSharedPreferences("data", MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();
        editor.putString("data_1", "DATA_1");
        editor.putString("data_2", "DATA_2");
        editor.apply();
        TextView textView2 = (TextView)((MainActivity)appContext).findViewById(R.id.textView2);
        textView2.setText(pref.getString("data_2", "---"));
        MainActivity.testTest();
        TestClass test_class = new TestClass();
        test_class.SampleTest();
    }

    // サブクラス
    private class TestClass {
        public void SampleTest() {
            System.out.println("Hello!!");
        }
    }

}