getHour() 方法中的致命错误

我想创建一个简单的闹钟，但我不知道为什么应用程序在calendar.set(Calendar.HOUR_OF_DAY, timePicker.getHour());. 一切似乎都按照说明进行。

import android.annotation.TargetApi;
import android.app.AlarmManager;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TimePicker;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {
    TimePicker timePicker;
    Button button;
    AlarmManager alarmManager;
    Calendar calendar;

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

        timePicker = (TimePicker) findViewById(R.id.timpik);
        button = (Button) findViewById(R.id.bpik);
        alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

        calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY, timePicker.getHour());
        calendar.set(Calendar.MINUTE, timePicker.getMinute());

    }
}

这是布局文件的样子

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.administrator.myapplication.MainActivity">

    <TimePicker
        android:id="@+id/timpik"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <Button
        android:id="@+id/bpik"
        android:text="Start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>