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TabLayout tabLayout;
AppBarLayout appBarLayout;
ViewPager viewPager;

tabLayout = findViewById(R.id.tab_layout);
appBarLayout = findViewById(R.id.appBar);
viewPager = findViewById(R.id.pager);

ViewPagerAdapter adapter= new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new pendingTasks(), "Pending");
adapter.addFragment(new currentTasks(), "OnGoing");
adapter.addFragment(new completedTasks(), "Completed");
viewPager.setAdapter(adapter);
tabLayout.setupWithViewPager(viewPager);

class ViewPagerAdapter extends FragmentPagerAdapter {

    private final List < Fragment > fragmentList = new ArrayList < > ();
    private final List < String > fragmentListTitles = new ArrayList < > ();
    public ViewPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return fragmentListTitles.get(position);
    }

    public void addFragment(Fragment fragment, String title) {
        fragmentList.add(fragment);
        fragmentListTitles.add(title);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="15dp"
            android:textColor="#ffffff"
            android:text="TODO Tasks"
            android:background="#424242"
            android:textAppearance="@android:style/TextAppearance.Material.Widget.ActionBar.Title"
            android:textSize="24sp" />

    </android.support.design.widget.AppBarLayout>


    <android.support.design.widget.TabLayout
        android:id="@+id/tab_layout"
        android:layout_width="374dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/appBar"
        app:layout_constraintVertical_bias="0.0"
        app:tabGravity="fill"
        app:tabMode="fixed" />

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="501dp"
        tools:layout_editor_absoluteX="101dp"
        tools:layout_editor_absoluteY="178dp" />

</LinearLayout>