エラー　シンボルを見つけられません

(R.id.content,new〜〜〜〜...の

contentにエラー出て
シンボルを見つけられません
となってしまいます。

どう対処すれば直りますでしょうか？
アドバイスお願いいたします。mm

java
1
2MainActivity
3
4import android.os.Bundle;
5import android.support.annotation.NonNull;
6import android.support.design.widget.BottomNavigationView;
7import android.support.v4.app.FragmentManager;
8import android.support.v4.app.FragmentTransaction;
9import android.support.v7.app.AppCompatActivity;
10import android.view.MenuItem;
11
12
13public class MainActivity extends AppCompatActivity {
14
15    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
16            = new BottomNavigationView.OnNavigationItemSelectedListener() {
17
18        @Override
19        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
20            FragmentManager fragmentManager = getSupportFragmentManager();
21            FragmentTransaction transaction = fragmentManager.beginTransaction();
22            switch (item.getItemId()) {
23                case R.id.navigation_product:
24                    transaction.replace(R.id.content,new Product()).commit();
25                    return true;
26                case R.id.navigation_cart:
27                    transaction.replace(R.id.content,new Cart()).commit();
28                    return true;
29                case R.id.navigation_delivery_status:
30                    transaction.replace(R.id.content,new DeliveryStatus()).commit();
31                    return true;
32                case R.id.navigation_mypage:
33                    transaction.replace(R.id.content,new Mypage()).commit();
34                    return true;
35            }
36            return false;
37        }
38    };
39
40    @Override
41    protected void onCreate(Bundle savedInstanceState) {
42        super.onCreate(savedInstanceState);
43        setContentView(R.layout.activity_main);
44
45        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
46        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
47
48        FragmentManager fragmentManager = getSupportFragmentManager();
49        FragmentTransaction transaction = fragmentManager.beginTransaction();
50        transaction.replace(R.id.content,new Product()).commit();
51    }
52
53}