java.lang.RuntimeException setOnClickListener (this);

Question

мой проект java.lang.RuntimeException Пожалуйста, отметьте и помогите мне, я хочу, чтобы фрагмент использовался, когда комментарий tab1.setOnClickListener (this);tab2.setOnClickListener (это);он не программирует, он работает. Открытый класс MainActivity расширяет AppCompatActivity, реализует View.OnClickListener {FragmentManagergmentManager;Кнопка tab1, tab2;

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

    fragmentManager = getSupportFragmentManager();

    tab1=findViewById(R.id.btnF1);
    tab2=findViewById(R.id.btnfr2);

    tab1.setOnClickListener(this);
    tab2.setOnClickListener(this);

    FragmentTransaction transaction = fragmentManager.beginTransaction();
    transaction.add(R.id.connteyner , new FragmentFirst())
            .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
            .addToBackStack("a")
            .commit();

}

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.btnF1:{
            replacefragment(new FragmentFirst());
            break;
        }
        case R.id.btnfr2:{
            replacefragment(new FragmentSecend());
            break;
        }

    }
}
private void replacefragment(Fragment fragment){
    FragmentTransaction transaction = fragmentManager.beginTransaction();
    transaction.replace(R.id.connteyner , fragment)
            .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
            .addToBackStack("a")
            .commit();
}

}

ошибка

2019-10-27 16:33:40.948 5560-5560/hhh.hhhh.daynamicfragment E/AndroidRuntime: FATAL EXCEPTION: main
Process: hh.hhhcode.daynamicfragment, PID: 5560
java.lang.RuntimeException: Unable to start activity ComponentInfo{hh.hhh.daynamicfragment/hh.hhh.daynamicfragment.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6077)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at hh.hhhh.daynamicfragment.MainActivity.onCreate(MainActivity.java:27)
    at android.app.Activity.performCreate(Activity.java:6662)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6077) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)