アプリがすぐに落ちてしまいます。

前提・実現したいこと

Android studioにてアラームを自分で設定し、その時間に通知が来るというのを実装したいのですが、アプリを起動したところすぐにアプリが落ちてしまいます。

該当のソースコード

Java
ソースコード　↓
MainActivity

package com.example.notification;

import androidx.appcompat.app.AppCompatActivity;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.Calendar;
import java.util.Locale;

import static java.lang.String.format;

public class MainActivity extends AppCompatActivity {

        private AlarmManager am;
        private PendingIntent pending;
        private int requestCode = 1;


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

            Button buttonStart = this.findViewById(R.id.button_start);
            buttonStart.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Calendar calendar;
                    calendar = Calendar.getInstance();
                    calendar.setTimeInMillis(System.currentTimeMillis());

                    calendar.add(Calendar.SECOND, Integer.parseInt(time));

                    Intent intent = new Intent(getApplicationContext(), AlarmNotification.class);
                    intent.putExtra("RequestCode",requestCode);

                    pending = PendingIntent.getBroadcast(
                            getApplicationContext(),requestCode, intent, 0);

                    // アラームをセットする
                    am = (AlarmManager) getSystemService(ALARM_SERVICE);

                    if (am != null) {
                        am.setExact(AlarmManager.RTC_WAKEUP,
                                calendar.getTimeInMillis(), pending);

                        // トーストで設定されたことをを表示
                        Toast.makeText(getApplicationContext(),
                                "alarm start", Toast.LENGTH_SHORT).show();

                        Log.d("debug", "start");
                    }
                }
            });

            // アラームの取り消し
            Button buttonCancel = findViewById(R.id.button_cancel);
            buttonCancel.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent indent = new Intent(getApplicationContext(), AlarmNotification.class);
                    PendingIntent pending = PendingIntent.getBroadcast(
                            getApplicationContext(), requestCode, indent, 0);

                    // アラームを解除する
                    AlarmManager am = (AlarmManager)MainActivity.this.
                            getSystemService(ALARM_SERVICE);
                    if (am != null) {
                        am.cancel(pending);
                        Toast.makeText(getApplicationContext(),
                                "alarm cancel", Toast.LENGTH_SHORT).show();
                        Log.d("debug", "cancel");
                    }
                    else{
                        Log.d("debug", "null");
                    }
                }
            });
        }
        EditText settingsTime = findViewById(R.id.jikoku);
        String time = settingsTime.getText().toString();
}

AlarmNotification

package com.example.notification;

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.media.RingtoneManager;
import android.net.Uri;
import android.util.Log;
import java.text.SimpleDateFormat;
import java.util.Locale;

public class AlarmNotification extends BroadcastReceiver{
@Override // データを受信した
public void onReceive(Context context, Intent intent) {

    Log.d("AlarmBroadcastReceiver","onReceive() pid=" + android.os.Process.myPid());

    int requestCode = intent.getIntExtra("RequestCode",0);

    PendingIntent pendingIntent =
            PendingIntent.getActivity(context, requestCode, intent, PendingIntent.FLAG_UPDATE_CURRENT);

    String channelId = "default";
    // app name
    String title = context.getString(R.string.app_name);

    long currentTime = System.currentTimeMillis();
    SimpleDateFormat dataFormat =
            new SimpleDateFormat("HH:mm:ss", Locale.JAPAN);
    String cTime = dataFormat.format(currentTime);

    // メッセージ　+ 11:22:331
    String message = "時間になりました。 "+cTime ;

    NotificationManager notificationManager =
            (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);

    Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

    // Notification　Channel 設定
    NotificationChannel channel = new NotificationChannel(
            channelId, title , NotificationManager.IMPORTANCE_DEFAULT);
    channel.setDescription(message);
    channel.enableVibration(true);
    channel.canShowBadge();
    channel.enableLights(true);
    channel.setLightColor(Color.BLUE);
    // the channel appears on the lockscreen
    channel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
    channel.setSound(defaultSoundUri, null);
    channel.setShowBadge(true);

    if(notificationManager != null){
        notificationManager.createNotificationChannel(channel);

        Notification notification = new Notification.Builder(context, channelId)
                .setContentTitle(title)
                // android標準アイコンから
                .setSmallIcon(android.R.drawable.ic_lock_idle_alarm)
                .setContentText(message)
                .setAutoCancel(true)
                .setContentIntent(pendingIntent)
                .setWhen(System.currentTimeMillis())
                .build();

        // 通知
        notificationManager.notify(R.string.app_name, notification);

    }
}

}