private void onClickVerifyPhoneNumber()

in auth/app/src/main/java/com/google/firebase/quickstart/auth/java/MultiFactorEnrollFragment.java [70:130]
50 lines of code
2 McCabe index (conditional complexity)

    private void onClickVerifyPhoneNumber() {
        String phoneNumber = mBinding.fieldPhoneNumber.getText().toString();

        OnVerificationStateChangedCallbacks callbacks =
                new OnVerificationStateChangedCallbacks() {
                    @Override
                    public void onVerificationCompleted(PhoneAuthCredential credential) {
                        // Instant-validation has been disabled (see requireSmsValidation below).
                        // Auto-retrieval has also been disabled (timeout is set to 0).
                        // This should never be triggered.
                        throw new RuntimeException(
                                "onVerificationCompleted() triggered with instant-validation and auto-retrieval disabled.");
                    }

                    @Override
                    public void onCodeSent(
                            final String verificationId, PhoneAuthProvider.ForceResendingToken token) {
                        Log.d(TAG, "onCodeSent:" + verificationId);
                        Toast.makeText( getContext(), "SMS code has been sent", Toast.LENGTH_SHORT)
                                .show();

                        mCodeVerificationId = verificationId;
                    }

                    @Override
                    public void onVerificationFailed(FirebaseException e) {
                        Log.w(TAG, "onVerificationFailed ", e);
                        Toast.makeText(getContext(), "Verification failed: " + e.getMessage(), Toast.LENGTH_SHORT)
                                .show();
                    }
                };

        FirebaseAuth.getInstance()
                .getCurrentUser()
                .getMultiFactor()
                .getSession()
                .addOnCompleteListener(
                        new OnCompleteListener<MultiFactorSession>() {
                            @Override
                            public void onComplete(@NonNull Task<MultiFactorSession> task) {
                                if (task.isSuccessful()) {
                                    PhoneAuthOptions phoneAuthOptions =
                                            PhoneAuthOptions.newBuilder()
                                                    .setPhoneNumber(phoneNumber)
                                                    // A timeout of 0 disables SMS-auto-retrieval.
                                                    .setTimeout(0L, TimeUnit.SECONDS)
                                                    .setMultiFactorSession(task.getResult())
                                                    .setCallbacks(callbacks)
                                                    // Disable instant-validation.
                                                    .requireSmsValidation(true)
                                                    .build();

                                    PhoneAuthProvider.verifyPhoneNumber(phoneAuthOptions);
                                } else {
                                    Toast.makeText(getContext(),
                                            "Failed to get session: " + task.getException(), Toast.LENGTH_SHORT)
                                            .show();
                                }
                            }
                        });
    }