Android StudioでNullPointerExceptionのエラー

Android Studioで、教材を参考に簡単な計算結果を表示するだけのアプリを作成してみたのですが、
後述するエラーがコンソールに表示されてしまいます。
NullPointerExceptionなのですが、何度コードを見返しても、エラー原因が突き止められません。
大変お手数ではございますが、ご回答頂けますと幸いです。

MainActivity.java

MainActivity.java
1package com.example.variables;
2
3import androidx.appcompat.app.AppCompatActivity;
4
5import android.os.Bundle;
6import android.util.Log;
7import android.widget.TextView;
8
9public class MainActivity extends AppCompatActivity {
10
11    @Override
12    protected void onCreate(Bundle savedInstanceState) {
13        super.onCreate(savedInstanceState);
14        setContentView(R.layout.activity_main);
15        
16        TextView text = findViewById(R.id.text);
17
18        int sumTwoIntegerNumber = 10 + 5;
19        text.setText(sumTwoIntegerNumber + "");
20
21    }
22}

activity_main.xml

activity_main.xml
1<?xml version="1.0" encoding="utf-8"?>
2<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
3    xmlns:app="http://schemas.android.com/apk/res-auto"
4    xmlns:tools="http://schemas.android.com/tools"
5    android:layout_width="match_parent"
6    android:layout_height="match_parent"
7    tools:context=".MainActivity">
8
9    <TextView
10        android:layout_width="wrap_content"
11        android:layout_height="wrap_content"
12        android:text="Hello World!"
13        android:textSize="30sp"
14        app:layout_constraintBottom_toBottomOf="parent"
15        app:layout_constraintLeft_toLeftOf="parent"
16        app:layout_constraintRight_toRightOf="parent"
17        app:layout_constraintTop_toTopOf="parent" />
18
19</androidx.constraintlayout.widget.ConstraintLayout>

エラー表示
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.variables, PID: 30979
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.variables/com.example.variables.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3431)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7660)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.variables.MainActivity.onCreate(MainActivity.java:19)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3404)