Вылетает приложение при нажатии на кнопку Android Studio

2 активити, на одном кнопка работает, на другом нет Конроллер работающего активити

    package com.baobabGames.physicshelperbook;
    import androidx.appcompat.app.AppCompatActivity;
     import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    public class MainActivity extends AppCompatActivity {
     public Button sevenb, eightb, nineb, tenb, elevenb;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sevenb = findViewById(R.id.button1);
        eightb = findViewById(R.id.button2);
        nineb = findViewById(R.id.button3);
        tenb = findViewById(R.id.button4);
        elevenb = findViewById(R.id.button5);
    }
     public void seven(View view) {
         setContentView(R.layout.seven);
     }
     public void eight(View view) {
         setContentView(R.layout.seven);
     }
     public void nine(View view) {
         System.out.println("--");
     }
     public void ten(View view) {
         System.out.println("--");
     }
     public void eleven(View view) {
         System.out.println("--");
     }
     }

Xml работающего активити

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button3"
        android:layout_width="326dp"
        android:layout_height="95dp"
        android:layout_marginTop="20dp"
        android:text="@string/_9_class"
        android:textSize="36sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.505"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button2" />

    <Button
        android:id="@+id/button4"
        android:layout_width="326dp"
        android:layout_height="95dp"
        android:layout_marginTop="20dp"
        android:text="@string/_10_class"
        android:textSize="36sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button3" />

    <Button
        android:id="@+id/button5"
        android:layout_width="326dp"
        android:layout_height="95dp"
        android:layout_marginTop="20dp"
        android:text="@string/_11_class"
        android:textSize="36sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.494"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button4" />

    <Button
        android:id="@+id/button1"
        android:layout_width="326dp"
        android:layout_height="95dp"
        android:layout_marginTop="28dp"
        android:onClick="seven"
        android:text="@string/_7_class"
        android:textSize="36sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.494"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="326dp"
        android:layout_height="95dp"
        android:layout_marginTop="20dp"
        android:onClick="eight"
        android:text="@string/_8_class"
        android:textSize="36sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.494"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button1" />
</androidx.constraintlayout.widget.ConstraintLayout>

Контроллер не работающего активити

package com.baobabGames.physicshelperbook;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.PersistableBundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

public class SevenControl extends AppCompatActivity {
    public Button b;
    @Override
    public void onCreate(Bundle persistentState) {
        super.onCreate(persistentState);
        setContentView(R.layout.seven);
        b=  (Button) findViewById(R.id.button);
    }

    @SuppressLint("SetTextI18n")
    public void bb(View view) {
        //setContentView(R.layout.activity_main);
        b.setText("fffffff");
    }

//    public void bb(View view) {
        //setContentView(R.layout.activity_main);
  //  }
}

Xml неработающего активити

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/linearLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".SevenControl"
    >


    <Spinner
        android:id="@+id/spinner"
        android:layout_width="409dp"
        android:layout_height="82dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="334dp"
        android:layout_height="544dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="56dp"
        android:text="@string/textview"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.36"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/spinner" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="116dp"
        android:onClick="bb"
        android:text="@string/button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>