Lacerta/app/src/main/java/one/nem/lacerta/MainActivity.java

package one.nem.lacerta;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentManager;
import androidx.navigation.NavController;
import androidx.navigation.fragment.NavHostFragment;
import androidx.navigation.ui.NavigationUI;

import android.os.Bundle;

import com.google.android.material.bottomnavigation.BottomNavigationView;

public class MainActivity extends AppCompatActivity {

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

        // デバッグ
        FragmentManager supportFragmentManager = getSupportFragmentManager();
        NavHostFragment navHostFragment =
                (NavHostFragment) supportFragmentManager.findFragmentById(R.id.nav_host_fragment);
        NavController navController = navHostFragment.getNavController();
        BottomNavigationView bottomNav = findViewById(R.id.nav_view);

        NavigationUI.setupWithNavController(bottomNav, navController);

        // デバッグ

    }
}