XML : i am trying to implementing customs toolbar with tab but it shows Null Pointer Execption [duplicate]

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• What is a Null Pointer Exception, and how do I fix it? 12 answers

Main Java Class with Toolbar Viewpager and Tablayout ..when i run the application its showing me the null pointer execption ...error is E/e: exptionjava.lang.NullPointerException

  public class MainActivity extends AppCompatActivity  {     Toolbar toolbar;      ViewPager mpager,viewPager;       TabLayout tabLayout;        ViewPagerAdapter viewPagerAdapter;        @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.activitymain_appbar);          toolbar = (Toolbar) findViewById(R.id.appbar);          viewPager = (ViewPager) findViewById(R.id.viewpager);          tabLayout = (TabLayout) findViewById(R.id.tablayout);          setSupportActionBar(toolbar);          getSupportActionBar().setDisplayShowHomeEnabled(true);          NavigtionDawrableActivity navigtionDawrableActivity = (NavigtionDawrableActivity)                  getSupportFragmentManager().findFragmentById(R.id.fragment_navigtion_dawrable);          navigtionDawrableActivity.setUp(R.id.fragment_navigtion_dawrable, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar);          mpager = (ViewPager) findViewById(R.id.pager);            viewPagerAdapter = new             ViewPagerAdapter(getSupportFragmentManager());          viewPagerAdapter.addfragments(new HomeFragments(), "Home");          viewPagerAdapter.addfragments(new PlayList_Page(), "Play List");              viewPager.setAdapter(viewPagerAdapter);              tabLayout.setupWithViewPager(viewPager);}    

set a adapter class

  public class ViewPagerAdapter extends FragmentPagerAdapter {        ArrayList<Fragment> fragments = new ArrayList<>();      ArrayList<String> tabtitle = new ArrayList<>();      public  void addfragments(Fragment fragments,String titles)      {          this.fragments.add(fragments);          this.tabtitle.add(titles);      }          public ViewPagerAdapter(FragmentManager fm) {          super(fm);      }        @Override      public Fragment getItem(int position) {          return fragments.get(position);      }        @Override      public int getCount() {          return fragments.size();      }        @Override      public CharSequence getPageTitle(int position) {          return tabtitle.get(position);      }  }    

Main Xml

   <LinearLayout          android:layout_width="match_parent"          android:layout_height="match_parent"          android:fitsSystemWindows="true"          android:orientation="vertical"          tools:context="com.example.zeenat.e_learning_app.MainActivity">            <android.support.design.widget.AppBarLayout              android:layout_width="match_parent"              android:layout_height="wrap_content">                <include                  android:id="@+id/appbar"                  layout="@layout/toolbar"                  android:layout_width="match_parent"                  android:layout_height="wrap_content" />                <android.support.design.widget.TabLayout                  android:id="@+id/tablayout"                  android:layout_width="match_parent"                  android:layout_height="wrap_content"                  app:tabMode="fixed"                  app:tabGravity="fill"                  android:background="#000"                  >              </android.support.design.widget.TabLayout>          </android.support.design.widget.AppBarLayout>         <android.support.v4.view.ViewPager             android:id="@+id/viewpager"             android:layout_width="match_parent"             android:layout_height="match_parent"             ></android.support.v4.view.ViewPage>      </LinearLayout>