1. activity_main.xml 코드

<androidx.appcompat.widget.LinearLayoutCompat
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <androidx.appcompat.widget.LinearLayoutCompat
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <Chronometer
            android:id="@+id/chronometer1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:format="예약에 걸린 시간  %s"
            android:textSize="20dp" />
        <androidx.appcompat.widget.AppCompatButton
            android:id="@+id/btnStart"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="예약 시작" />
    </androidx.appcompat.widget.LinearLayoutCompat>

    <RadioGroup
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <RadioButton
            android:id="@+id/rbCal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="날짜 설정(캘린더뷰)" />
        <RadioButton
            android:id="@+id/rbTime"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="시간 설정" />
    </RadioGroup>

    <androidx.appcompat.widget.LinearLayoutCompat
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_weight="1">
        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <CalendarView
                android:id="@+id/calendarView1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"/>
            <TimePicker
                android:id="@+id/timePicker1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"/>
        </FrameLayout>
    </androidx.appcompat.widget.LinearLayoutCompat>

    <androidx.appcompat.widget.LinearLayoutCompat
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <androidx.appcompat.widget.AppCompatButton
            android:id="@+id/btnEnd"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="예약완료" />
        <TextView
            android:id="@+id/tvYear"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0000"/>
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="년"/>
        <TextView
            android:id="@+id/tvMonth"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="00"/>
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="월"/>
        <TextView
            android:id="@+id/tvDay"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="00"/>
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="일"/>
        <TextView
            android:id="@+id/tvHour"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="00"/>
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="시"/>
        <TextView
            android:id="@+id/tvMinute"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="00"/>
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="분 예약됨"/>
    </androidx.appcompat.widget.LinearLayoutCompat>
</androidx.appcompat.widget.LinearLayoutCompat>

2. MainActivity.java 코드

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity2";

    private Chronometer chronometer1;
    private Button btnStart, btnEnd;
    private RadioButton rbCal, rbTime;
    private CalendarView calendarView1;
    private TimePicker timePicker1;
    private TextView tvYear, tvMonth, tvDay, tvHour, tvMinute;
    int selectYear, selectMonth, selectDay;

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

        init();
        initLr();
        initData();
    }

    public void init(){
        chronometer1 = findViewById(R.id.chronometer1);
        btnStart = findViewById(R.id.btnStart);
        btnEnd = findViewById(R.id.btnEnd);
        rbCal = findViewById(R.id.rbCal);
        rbTime = findViewById(R.id.rbTime);
        calendarView1 = findViewById(R.id.calendarView1);
        timePicker1 = findViewById(R.id.timePicker1);
        tvYear = findViewById(R.id.tvYear);
        tvMonth = findViewById(R.id.tvMonth);
        tvDay = findViewById(R.id.tvDay);
        tvHour = findViewById(R.id.tvHour);
        tvMinute = findViewById(R.id.tvMinute);

        timePicker1.setVisibility(View.INVISIBLE);
        calendarView1.setVisibility(View.INVISIBLE);
    }
    public void initLr(){
        rbCal.setOnClickListener(v -> {
            timePicker1.setVisibility(View.INVISIBLE);
            calendarView1.setVisibility(View.VISIBLE);
        });
        rbTime.setOnClickListener(v -> {
            timePicker1.setVisibility(View.VISIBLE);
            calendarView1.setVisibility(View.INVISIBLE);
        });

        btnStart.setOnClickListener(v -> {
            chronometer1.setBase(SystemClock.elapsedRealtime());
            chronometer1.start();
            chronometer1.setTextColor(Color.RED);
        });
        btnEnd.setOnClickListener(v -> {
            chronometer1.stop();
            chronometer1.setTextColor(Color.BLUE);
        });
        calendarView1.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
            @Override
            public void onSelectedDayChange(CalendarView calendarView1, 
            					int year, int month, int dayOfMonth) {
                selectYear = year;
                selectMonth = month + 1;
                selectDay = dayOfMonth;
            }
        });
    }
    public void initData(){
        tvYear.setText(Integer.toString(selectYear));
        tvMonth.setText(Integer.toString(selectMonth));
        tvDay.setText(Integer.toString(selectDay));

        tvHour.setText(Integer.toString(timePicker1.getCurrentHour()));
        tvMinute.setText(Integer.toString(timePicker1.getCurrentMinute()));
    }
}