Ошибка с использованием нескольких Activity

public class MainActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
 
    public void ButtonClick(View view) {
        Intent intent = new Intent(this, SecondActivity.class);
        startActivity(intent);
    }
}

E/AndroidRuntime: FATAL EXCEPTION: main
Process: my.com.timetable, PID: 29300
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:4764)
at android.view.View$PerformClick.run(View.java:19844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5356)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:4764)*
at android.view.View$PerformClick.run(View.java:19844)*
at android.os.Handler.handleCallback(Handler.java:739)*
at android.os.Handler.dispatchMessage(Handler.java:95)*
at android.os.Looper.loop(Looper.java:135)*
at android.app.ActivityThread.main(ActivityThread.java:5356)*
at java.lang.reflect.Method.invoke(Native Method)*
at java.lang.reflect.Method.invoke(Method.java:372)*
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)*
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)*
Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {my.com.timetable/my.com.timetable.MondayActivity}; have you declared this activity in your AndroidManifest.xml?
at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1761)
at android.app.Instrumentation.execStartActivity(Instrumentation.java:1485)
at android.app.Activity.startActivityForResult(Activity.java:3824)
at android.app.Activity.startActivityForResult(Activity.java:3785)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:842)
at android.app.Activity.startActivity(Activity.java:4095)
at android.app.Activity.startActivity(Activity.java:4063)
at my.com.timetable.MainActivity.onMondayClicked(MainActivity.java:18)
at java.lang.reflect.Method.invoke(Native Method)*
at java.lang.reflect.Method.invoke(Method.java:372)*
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)*
at android.view.View.performClick(View.java:4764)*
at android.view.View$PerformClick.run(View.java:19844)*
at android.os.Handler.handleCallback(Handler.java:739)*
at android.os.Handler.dispatchMessage(Handler.java:95)*
at android.os.Looper.loop(Looper.java:135)*
at android.app.ActivityThread.main(ActivityThread.java:5356)*
at java.lang.reflect.Method.invoke(Native Method)*
at java.lang.reflect.Method.invoke(Method.java:372)*
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)*
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)*