[ADD] bottomNav functionality

TODO: change placeholder icons

app/src/main/java/com/a1/nextlocation/MainActivity.java

@@ -1,13 +1,21 @@
 package com.a1.nextlocation;
 
+import androidx.annotation.NonNull;
 import androidx.appcompat.app.AppCompatActivity;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentTransaction;
 
 import android.os.Bundle;
+import android.view.MenuItem;
 
 import com.a1.nextlocation.R;
+import com.a1.nextlocation.fragments.HomeFragment;
+import com.a1.nextlocation.fragments.RouteFragment;
+import com.a1.nextlocation.fragments.SettingsFragment;
+import com.a1.nextlocation.fragments.StatisticFragment;
+import com.google.android.material.bottomnavigation.BottomNavigationView;
 
 public class MainActivity extends AppCompatActivity {
-
     /**
      * onCreate method that creates the main activity
      * @param savedInstanceState the saved instance state of the app
@@ -16,5 +24,33 @@ public class MainActivity extends AppCompatActivity {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
+
+        BottomNavigationView bottomNav = findViewById(R.id.navbar);
+        bottomNav.setOnNavigationItemSelectedListener(navListener);
+
+        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_layout, new HomeFragment()).commit();
     }
+
+
+    private BottomNavigationView.OnNavigationItemSelectedListener navListener = item -> {
+        Fragment selectedFragment = null;
+
+        switch (item.getItemId()) {
+            case R.id.locations:
+                selectedFragment = new HomeFragment();
+                break;
+            case R.id.routes:
+                selectedFragment = new RouteFragment();
+                break;
+            case R.id.statistics:
+                selectedFragment = new StatisticFragment();
+                break;
+            case R.id.settings:
+                selectedFragment = new SettingsFragment();
+                break;
+        }
+
+        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_layout, selectedFragment).commit();
+        return true;
+    };
 }