无法取回保存在 SharedPreference 中的数据

private RadioGroup rgTravel;
SharedPreferences sharedPreferences;
private static final String PREFS = "PREFS";
private static final String Travel = "travel";
private RadioButton radioButton;
String travel;

@Override
protected void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activity2);


    final Button btnOk = (Button)findViewById(R.id.btnOk);
    btnOk.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            Intent activity3 = new Intent(MainActivity2Activity.this, MainActivity3Activity.class);


            rgTravel = (RadioGroup) findViewById(R.id.rgTravel);
            int selectedId = rgTravel.getCheckedRadioButtonId();
            radioButton = (RadioButton) findViewById(selectedId);
            travel = radioButton.getText().toString();

            SharedPreferences preferences-= PreferenceManager.getDefaultSharedPreferences(MainActivity2Activity.this);
            SharedPreferences.Editor editor = preferences.edit();
            editor.putString(Travel, travel);
            editor.commit();


            Toast.makeText(getApplicationContext(), travel, Toast.LENGTH_LONG).show();
            startActivity(activity3);

        }

    });
}

这是我的activity2，我应该在这里创建共享首选项，并保存用户的选择。（我想将用户的选择保存在无线电组中）查看我的活动 3，我应该在那里取回选择：

public void onCreate(Bundle savedInstanceState) {

    String choice;
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activity3);

        SharedPreferences PREFS = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        choice = PREFS.getString("Travel", "Beach");
        Toast.makeText(getApplicationContext(), choice, Toast.LENGTH_LONG).show();
        displayPicture(choice);


        Button next = (Button) findViewById(R.id.button3);
        next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent activity4 = new Intent(MainActivity3Activity.this, MainActivity4Activity.class);
                startActivity(activity4);
            }
        });
    }

我在每个活动中都创建了一个 Toast，以确保问题确实与偏好有关，而不是与其他步骤有关。