how to change fragment on button click navigation drawer

1import android.os.Bundle;
2import android.support.design.widget.FloatingActionButton;
3import android.support.design.widget.Snackbar;
4import android.view.View;
5import android.support.design.widget.NavigationView;
6import android.support.v4.view.GravityCompat;
7import android.support.v4.widget.DrawerLayout;
8import android.support.v7.app.ActionBarDrawerToggle;
9import android.support.v7.app.AppCompatActivity;
10import android.support.v7.widget.Toolbar;
11import android.view.Menu;
12import android.view.MenuItem;
13import android.support.v4.app.Fragment;
14import android.support.v4.app.FragmentManager;
15import android.support.v4.app.FragmentTransaction;
16
17public class MainActivity extends AppCompatActivity
18        implements NavigationView.OnNavigationItemSelectedListener {
19
20    @Override
21    protected void onCreate(Bundle savedInstanceState) {
22        super.onCreate(savedInstanceState);
23        setContentView(R.layout.activity_main);
24        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
25        setSupportActionBar(toolbar);
26
27        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
28        fab.setOnClickListener(new View.OnClickListener() {
29            @Override
30            public void onClick(View view) {
31                Snackbar.make(view, "bryanposvoc1339.garcia@gmail.com", Snackbar.LENGTH_LONG)
32                        .setAction("Action", null).show();
33            }
34        });
35
36        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
37        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
38                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
39        drawer.setDrawerListener(toggle);
40        toggle.syncState();
41
42        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
43        navigationView.setNavigationItemSelectedListener(this);
44    }
45
46    @Override
47    public void onBackPressed() {
48        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
49        if (drawer.isDrawerOpen(GravityCompat.START)) {
50            drawer.closeDrawer(GravityCompat.START);
51        } else {
52            super.onBackPressed();
53        }
54    }
55
56    @Override
57    public boolean onCreateOptionsMenu(Menu menu) {
58        // Inflate the menu; this adds items to the action bar if it is present.
59        getMenuInflater().inflate(R.menu.main, menu);
60        return true;
61    }
62
63    @Override
64    public boolean onOptionsItemSelected(MenuItem item) {
65        // Handle action bar item clicks here. The action bar will
66        // automatically handle clicks on the Home/Up button, so long
67        // as you specify a parent activity in AndroidManifest.xml.
68        int id = item.getItemId();
69
70        //noinspection SimplifiableIfStatement
71        if (id == R.id.action_settings) {
72            return true;
73        }
74
75        return super.onOptionsItemSelected(item);
76    }
77
78    @SuppressWarnings("StatementWithEmptyBody")
79    @Override
80    public boolean onNavigationItemSelected(MenuItem item) {
81        int id = item.getItemId();
82        Fragment fragment;
83
84        if (id == R.id.nav_cough) {
85             fragment = new first();
86            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
87            ft.replace(R.id.mainFrame, fragment);
88            ft.commit();
89        }
90        else if (id == R.id.nav_colds) {
91              fragment = new second();
92            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
93            ft.replace(R.id.mainFrame, fragment);
94            ft.commit();
95        }
96        else if (id == R.id.nav_fever) {
97            fragment = new third();
98            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
99            ft.replace(R.id.mainFrame, fragment);
100            ft.commit();
101        }
102        else if (id == R.id.nav_vegetables) {
103            fragment = new fourth();
104            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
105            ft.replace(R.id.mainFrame, fragment);
106            ft.commit();
107        } else if (id == R.id.nav_fruits) {
108            fragment = new fifth();
109            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
110            ft.replace(R.id.mainFrame, fragment);
111            ft.commit();
112        } else if (id == R.id.nav_about) {
113            fragment = new sixth();
114            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
115            ft.replace(R.id.mainFrame, fragment);
116            ft.commit();
117        }
118        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
119        drawer.closeDrawer(GravityCompat.START);
120        return true;
121    }
122}
123