public class MainActivity extends AppCompatActivity {
    RadioButton radioButton2,radioButton3;
    SharedPreferences sharedPreferences=this.getPreferences(Context.MODE_PRIVATE);
    SharedPreferences.Editor editor=sharedPreferences.edit();
    String veri=sharedPreferences.getString("kullanici","");
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if(veri.equals(AppCompatDelegate.MODE_NIGHT_NO))
            radioButton2.setChecked(true);
        else
            radioButton3.setChecked(true);

    }
    public void onRadioClicked(View view){
        SharedPreferences sharedPreferences=this.getPreferences(Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=sharedPreferences.edit();
        String veri=sharedPreferences.getString("kullanici","");
        boolean checked=((RadioButton)view).isChecked();
        switch (view.getId()){
            case R.id.radioButton2:
                if(checked){
                    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
                    editor.putInt("tema",AppCompatDelegate.MODE_NIGHT_NO);
                    editor.apply();
                }
                break;
            case R.id.radioButton3:
                if(checked){
                    AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
                    editor.putInt("tema",AppCompatDelegate.MODE_NIGHT_YES);
                    editor.apply();
                }
                break;
        }
    }
    protected void onDestroy() {
        sharedPreferences=null;
        super.onDestroy();
    }

}