Error when multiplying java null values

Question

I’m having the following problem: In my project there are two fields (editText) where the user can or cannot enter the value.

Edittext that receives the amount etCount.

Edittext that receives the value etPriceUnit.

When the etCount and the etPriceUnit present the value "null" at the time of calculating the application closes.

This probably occurs in the attempt to convert to double and multiply null values on the line double doubleTOTAL_PRICE_ITEM = (Double.parseDouble(stringCOUNT) * Double.parseDouble(stringPRICE_UNIT));.

I tried the following to fix such problem:

if (stringCOUNT == null || stringPRICE_UNIT == null) {
    String stringTOTAL_PRICE_ITEM = "0";
} else {
    Double doubleTOTAL_PRICE_ITEM = (Double.parse.Double(stringCOUNT) * Double.parseDouble(stringPRICE_UNIT));
    String stringTOTAL_PRICE_ITEM = Double.toString(doubleTOTAL_PRICE_ITEM);
}

But I did not succeed. I cannot use the variable created within the if on the line result = crud.insertProduct(stringPRODUCT_NAME, stringCOUNT, stringPRICE_UNIT, stringTOTAL_PRICE_ITEM);.

Insertproduct.class (onClick):

public void onClick(View v) {

    Controller crud = new Controller(getBaseContext());
    EditText PRODUCT_NAME = (EditText) findViewById(R.id.etProductName);
    EditText COUNT = (EditText) findViewById(R.id.etCount);
    EditText PRICE_UNIT = (EditText) findViewById(R.id.etPriceUnit);

    String stringPRODUCT_NAME = PRODUCT_NAME.getText().toString();
    String stringCOUNT = COUNT.getText().toString();
    String stringPRICE_UNIT = PRICE_UNIT.getText().toString();
    double doubleTOTAL_PRICE_ITEM = (Double.parseDouble(stringCOUNT) * Double.parseDouble(stringPRICE_UNIT));
    String stringTOTAL_PRICE_ITEM = Double.toString(doubleTOTAL_PRICE_ITEM);
    String result;
    if (stringPRODUCT_NAME.matches("")) {
        Toast.makeText(InsertProduct.this, "Você não inseriu o nome do produto.", Toast.LENGTH_SHORT).show();
        return;
    }

    result = crud.insertProduct(stringPRODUCT_NAME, stringCOUNT, stringPRICE_UNIT, stringTOTAL_PRICE_ITEM);
    Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show();

    Intent intent = new Intent(InsertProduct.this, Main.class);
    startActivity(intent);
    finish();
}  

Controller.class (String insertProduct):

public String insertProduct(String PRODUCT_NAME, String stringCOUNT, String stringPRICE_UNIT, String stringTOTAL_PRICE_ITEM) {

    ContentValues values;
    long result;

    db = database.getWritableDatabase();
    values = new ContentValues();
    values.put(CreateDB.PRODUCT_NAME, PRODUCT_NAME);
    values.put(CreateDB.COUNT, stringCOUNT);
    values.put(CreateDB.PRICE_UNIT, stringPRICE_UNIT);
    values.put(CreateDB.TOTAL_PRICE_ITEM, stringTOTAL_PRICE_ITEM);

    result = db.insert(CreateDB.TABLE, null, values);
    db.close();

    if (result == -1)
        return "Erro ao inserir o produto.";
    else
        return "Produto inserido com sucesso!";
}

@Update Problem solved. Follows the solution.

String stringCOUNT = COUNT.getText().toString(); //Pegando o valor do etCount e convertendo para string
String stringPRICE_UNIT = PRICE_UNIT.getText().toString();

if (stringCOUNT.matches("")) { //Se o EditText estiver vazio faça
    doubleCOUNT = 0; //Atribui o valor 0 se o EditText estiver vazio
} else { //Senão
    doubleCOUNT = Double.parseDouble(stringCOUNT); //Pega o valor do EditText e converte para double
}

if (stringPRICE_UNIT.matches("")) {
    doublePRICE_UNIT = 0;
} else {
    doublePRICE_UNIT = Double.parseDouble(stringPRICE_UNIT);
}

Answer 1

Well to solve your problem I will give you a way to set the value 0 both to variable doubleCOUNT for the variable doublePRICE_UNIT when editText has nothing written.

Add the method addTextChangedListener() for your two editTexts (etCount and etPriceUnit) and do the following:

etCount:

etCount.addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

        if (s.length()>0){ //essa condição só executará se o editText não estiver vazio e fará com que seja adicionado o valor digitado no editText à variável doubleCOUNT

            doubleCOUNT=Double.parseDouble(etCount.getText().toString().trim());

        }else{ //essa condição fará com que seja atribuído o valor 0 à variável doubleCOUNT se não tiver nada escrito no editText (etCount)

            doubleCount=0;
            etCount.setHint("0");

        }

    }

    @Override
    public void afterTextChanged(Editable s) {

    }
});

Just do the same thing with etPriceUnit.

Remembering that you cannot (at least not for what you are trying to do), multiply strings, because STRINGS variables are not only prepared to receive numbers, but also letters and special digits.