TextView即使已初始化,也未初始化

我在这件事上失去了理智。我收到错误提示“变量'joiningDate'可能尚未初始化”。以下是代码:

private TextView joiningDate;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_registration);
        joiningDate = findViewById(R.id.joiningDate);
    }

private void saveData() {
        String name = editTextName.getText().toString();
        String email = editTextEmail.getText().toString();
        String phone = editTextPhone.getText().toString();
        String userId = editTextUserId.getText().toString();
        String password = editTextPassword.getText().toString();
        String joiningDate = joiningDate.getText().toString();

        // Now send this data to your server
        sendDataToServer(name, email, phone, userId, password, joiningDate);
    }

请帮我修一下。