Cannot resolve final FirebaseUser firebaseUser = FirebaseAuth.getInstance();

Cannot reolve

final FirebaseUser firebaseUser = FirebaseAuth.getInstance();

If I change it to

final FirebaseAuth firebaseAuth = FirebaseAuth.getInstance(); 

it won't resolve the getUid in this

if (!user.getUser_id().equals(firebaseUser.getUid())){
                    mUsers.add(user);

And if I change it to FirebaseUser firebaseUser = FirebaseUser.getInstance(); it wont resolve the getInstance(); What can I do to remove the error please help

    private void readUsers() {
        final FirebaseUser firebaseUser = FirebaseAuth.getInstance();
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference("users");

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                mUsers.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                    User user = snapshot.getValue(User.class);

                    assert user !=null;
                    assert firebaseUser !=null;
                    if (!user.getUser_id().equals(firebaseUser.getUid())){
                        mUsers.add(user);
                    }
                }
                userAdapter = new UserAdapter(getContext(), mUsers);
                recyclerView.setAdapter(userAdapter);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

FirebaseAuth.getInstance() returns an instance of FirebaseAuth, so this:

final FirebaseUser firebaseUser = FirebaseAuth.getInstance();

should be this instead:

final FirebaseAuth auth = FirebaseAuth.getInstance();

Then change this:

assert user !=null;
assert firebaseUser !=null;
if (!user.getUser_id().equals(firebaseUser.getUid())){
     mUsers.add(user);
 }

into this:

if (!user.getUser_id().equals(auth.getCurrentUser().getUid())){
     mUsers.add(user);
}