Android: Null pointer or not return anything

When i clicked a button, Textview not changing

Here my code:

BTNprint = findViewById(R.id.BTNprint);
        BTNprint.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String jmlobt = String.valueOf(ETjumlahobattransaksi1.getText().toString());
                TVcetakjumlah1.setText(jmlobt);
                String nmobt = String.valueOf(ETnamaobattransaksi1.getText().toString());
                TVcetaknama1.setText(nmobt);
                String ttlobt = String.valueOf(TVtotalobat1.getText().toString());
                TVcetaktotal1.setText(ttlobt);
            }
        });

ETjumlahobattransaksi1, ETnamaobattransaksi1, and TVtotalobat1 is from another class