public class MainActivity extends AppCompatActivity implements View.OnClickListener{

        EditText edtWidth, edtHeight, edtLength;
        Button btnCalculate;
        TextView tvResult;

        @Override
        protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        edtWidth = findViewById(R.id.edt_width);
        edtHeight = findViewById(R.id.edt_height);
        edtLength = findViewById(R.id.edt_length);
        btnCalculate = findViewById(R.id.btn_calculate);
        tvResult = findViewById(R.id.tv_result);

        btnCalculate.setOnClickListener(this);

        }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.btn_calculate){
            String inputLength = edtLength.getText().toString().trim();
            String inputWidth = edtWidth.getText().toString().trim();
            String inputHeight = edtHeight.getText().toString().trim();

            boolean isEmptyFields = false;
            boolean isInvalidDouble = false;

            if (TextUtils.isEmpty(inputLength)){
                isEmptyFields = true;
                edtLength.setError("Field Ini Tidak Boleh Kosong"
                );
            }
            if (TextUtils.isEmpty(inputWidth)){
                isEmptyFields = true;
                edtWidth.setError("Field Ini Tidak Boleh Kosong");
            }
            if (TextUtils.isEmpty(inputHeight)){
                isEmptyFields = true;
                edtHeight.setError("Field Ini Tidak Boleh Kosong");
            }

            Double length = toDouble (inputLength);
            Double width  = toDouble (inputWidth);
            Double height = toDouble (inputHeight);

            if (length == null) {
                isInvalidDouble = true;
                edtLength.setError("Field ini harus berupa nomer yang valid");
            }

            if (width == null) {
                isInvalidDouble = true;
                edtWidth.setError("Field ini harus berupa nomer yang valid");
            }

            if (height == null) {
                isInvalidDouble = true;
                edtHeight.setError("Field ini harus berupa nomer yang valid");
            }

            if (!isEmptyFields && !isInvalidDouble) {

                double volume = length * width * height;

                tvResult.setText(String.valueOf(volume));
            }
        }
    }

    private Double toDouble(String str) {
        try {
            return Double.valueOf(str);
        } catch (NumberFormatException e) {
            return null;
        }
    }
}