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Replace a Fragment with another from a separate java class

I have a Recycler View in a Fragment that I have an adapter class for in a separate file. I am trying to make it so that when you click on a RecyclerView Item it replaces the current fragment with a new one. The code to replace a fragment with another that I had been using previously is this:
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.nav_host_fragment, NewFragment.class, null);
transaction.addToBackStack("CurrentFragment");
transaction.commit();
And this works inside the fragment, but since I have to call it from the java class I tried this instead:
FragmentManager fragmentManager = ((AppCompatActivity) context).getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.nav_host_fragment, NewFragment.class, null);
transaction.addToBackStack("CurrentFragment");
transaction.commit();
And this just layers the new fragment on top of the current one. If I try making a class in the Current Fragment with the transaction code in it and call it, it doesn't work because of the static context.
Is there any way to do this?

removing fragment with popBackStack();

I have a few fragments in one activity. In Main Activity I implemented popBackStack(); in onBackPressed();
So that, you can always go back to previous fragment clicking back button. But popBackStack(); doesn't remove the fragment I just left.
How to achieve removing current fragment each time, we click back
button?

public void removeFragmentbyTag(String myFrag){
FragmentManager manager = getActivity().getSupportFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
trans.remove(myFrag);
trans.commit();
manager.popBackStack();
}
hope this bit of code help you.

Completely Refresh Fragment

I have a fragment and I need to completely refresh/reinstantiate it.
By refreshing I mean recreating fragment.
I have tried using FragmentManager with detach() method but it didn't help. All EditText children of that fragment still have their values entered even though the fragment was refreshed
Is there any way to achieve this result?

if there are only edit texts , create a method that sets all edit texts to empty string that is et(edit_text object),
et.setText(""); //edit text will be reset

Put the following code inside the fragment which need to be refreshed.
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.detach(this).attach(this).commit();
Use fragment manger according to your code (if it is an old version then this will be supportFragmentManager)

Put and call this method to your fragment
private void reloadFragment(){
Fragment frg = getActivity().getSupportFragmentManager().findFragmentByTag(ReceiptFragment.TAG);
final FragmentTransaction ft = getActivity().getSupportFragmentManager().beginTransaction();
ft.detach(frg);
ft.attach(frg);
ft.commit();
}

Opening fragment on clicking on Notification

I have one SplashActivity and one MainActivity and all the fragments are associated with MainActivity. Now whenever I recive Notification from server I want to open one specific fragment. I am opening this like
final android.support.v4.app.FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
if(getIntent().getAction().equals("OpenNotificationFragment")) {
fragmentManager.beginTransaction()
.replace(R.id.fragment_main_container, new NotificationFragment()).addToBackStack(PastOrderFragment.TAG)
.commitAllowingStateLoss();
}
but during my splash image is loading it is throwing NullPointerException, should I call this method in SplashActivity or edit some of my code.

Check if a fragment exists and reuse it

I'm using the following code to create a fragment everytime the user click on an item in a list view.
But in this way the fragment is created at every user click. What I want is to reuse the old fragment (if it exists) and only reload its content (don't create a new one).
MagazineViewFragment fragment = new MagazineViewFragment();
fragment.openStream(itemSelected);
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, fragment)
.commit();
How can I do?

There're multiple ways, probably the most easy one is to check if the current Fragment in your container is an instance of FragmentXYZ (in your case MagazineViewFragment).
Example
Fragment mFragment = getFragmentManager().findFragmentById(R.id.container);
if (mFragment instanceof MagazineViewFragment)
return;

Add tag when you call your fragment from activity:
FragmentManager fm = getFragmentManager();
Fragment fragment = fm.findFragmentByTag( MagazineViewFragment.TAG);
if (fragment == null) {
MagazineViewFragment fragment = new MagazineViewFragment();
fragment.openStream(itemSelected);
getFragmentManager()
.beginTransaction()
.add(R.id.container, fragment, MagazineViewFragment.TAG)
.commit();
}
If you need only to update itemSelected - see broadcasts or listeners.

Something like this might help:
getFragmentManager().findFragmentById(fragmentId);
Do not forget the null check.