How to achieve a full-screen dialog as described in material guidelines?

Use DialogFragment

Refer this link for Showing a Dialog Fullscreen or as an Embedded Fragment

http://developer.android.com/guide/topics/ui/dialogs.html#FullscreenDialog

I am just copying the code here.

Create a dialogfragment

    public class CustomDialogFragment extends DialogFragment {
    /** The system calls this to get the DialogFragment's layout, regardless
        of whether it's being displayed as a dialog or an embedded fragment. */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout to use as dialog or embedded fragment
        return inflater.inflate(R.layout.purchase_items, container, false);
    }

    /** The system calls this only when creating the layout in a dialog. */
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // The only reason you might override this method when using onCreateView() is
        // to modify any dialog characteristics. For example, the dialog includes a
        // title by default, but your custom layout might not need it. So here you can
        // remove the dialog title, but you must call the superclass to get the Dialog.
        Dialog dialog = super.onCreateDialog(savedInstanceState);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        return dialog;
    }
}

Then add this method to show the dialog

    public void showDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    CustomDialogFragment newFragment = new CustomDialogFragment();

    if (mIsLargeLayout) {
        // The device is using a large layout, so show the fragment as a dialog
        newFragment.show(fragmentManager, "dialog");
    } else {
        // The device is smaller, so show the fragment fullscreen
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        // For a little polish, specify a transition animation
        transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        // To make it fullscreen, use the 'content' root view as the container
        // for the fragment, which is always the root view for the activity
        transaction.add(android.R.id.content, newFragment)
                   .addToBackStack(null).commit();
    }
}

The main thing that has to be focused is in this line

transaction.add(android.R.id.content, newFragment).addToBackStack(null).commit();

The dialog become fullscreen when u specifiy the rootview as the android.R.id.content

The answer from Boss is correct, but missing the requested action bar as displayed on link in the question.

So, full example below.

Dialog fragment:

public class AKDialogFragment extends DialogFragment {

private static final String TAG = "AKDialogFragment";

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.dialog_ak, container, false);

    Toolbar toolbar = (Toolbar) rootView.findViewById(R.id.toolbar);
    toolbar.setTitle("Dialog title");

    ((AppCompatActivity) getActivity()).setSupportActionBar(toolbar);

    ActionBar actionBar = ((AppCompatActivity) getActivity()).getSupportActionBar();
    if (actionBar != null) {
        actionBar.setDisplayHomeAsUpEnabled(true);
        actionBar.setHomeButtonEnabled(true);
        actionBar.setHomeAsUpIndicator(android.R.drawable.ic_menu_close_clear_cancel);
    }
    setHasOptionsMenu(true);
    return rootView;
}

@NonNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    Dialog dialog = super.onCreateDialog(savedInstanceState);
    dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
    return dialog;
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    menu.clear();
    getActivity().getMenuInflater().inflate(R.menu.menu_ak, menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.action_save) {
        // handle confirmation button click here
        return true;
    } else if (id == android.R.id.home) {
        // handle close button click here
        dismiss();
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

Layout dialog_ak.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
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:fitsSystemWindows="true">

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay"/>

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

<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:background="#ffffff"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Your content here"/>

</LinearLayout>

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

Menu menu_ak.xml

<menu 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">
  <item
    android:id="@+id/action_save"
    android:orderInCategory="100"
    android:title="Save"
    app:showAsAction="always"/>
</menu>

Hosting activity must extend AppCompatActivity. Launching dialog is the same as in Boss answer:

FragmentManager fragmentManager = getSupportFragmentManager();
AKDialogFragment newFragment = new AKDialogFragment();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
transaction.add(android.R.id.content, newFragment).addToBackStack(null).commit();

I hope it helps someone.

try this code:

Dialog yourDialog=new Dialog(this,android.R.styleTheme_Black_NoTitleBar_Fullscreen)