Class must either be declared abstract or implement abstract method

package com.example.testapp2;
 
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
 
public abstract class FragmentContainer extends AppCompatActivity {
 
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_container);
        if (savedInstanceState == null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.fragmentContainer, getFragment())
                    .commit();
        }
    }
 
    protected abstract Fragment getFragment();
 
    @Override
    public void onBackPressed() {
        FragmentManager fragmentManager = getSupportFragmentManager();
        if (fragmentManager.getBackStackEntryCount() == 1) {
            finish();
        } else {
            fragmentManager.popBackStack();
        }
    }
}

package com.example.testapp2;
 
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;
 
public class MainActivity extends FragmentContainer{
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
 
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        return super.onCreateOptionsMenu(menu);
    }
 
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case R.id.setting:
                break;
            case R.id.search:
                break;
            case R.id.exit:
                break;
            default: break;
        }
        return super.onOptionsItemSelected(item);
    }
}