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Jordi Castilla
Asked: 2020-07-08 01:40:05 +0800 CST 2020-07-08 01:40:05 +0800 CST

Why contains(".") is 'true' but split(".") gives me an empty array?

  • 772

Let's take this method:

public static void getDecimalPart(double n) {
    int decimales = 0;

    // convertimos el valor a string
    String decimalPartString = String.valueOf(n);

    // comprobamos si contiene punto de decimales
    if (decimalPartString.contains(".")) { 
        // lo partimos y lo ponemos en un array
        String[] doubleArray = decimalPartString.split(".");
        // calculamos los decimales
        decimales = (int) (Double.valueOf(doubleArray[1]) * (Math.pow(10, doubleArray[1].length()-2)));
    }

    // imprimimos
    System.out.println("El numero " + n + " tiene " + decimales + " decimales");
}

It checks if the string contains(".") and if so it does split(".")... then... why when I run:

public static void main(String[] args) {
    getDecimalPart(1.25698);
}

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1 at q1607.Q38239413.getDecimalPart(Q38239413.java:25) at q1607.Q38239413.main(Q38239413.java:14)

Debugging even confuses me even more since the array is totally empty, it does not matter IOOBto ask for position 1 and that it does not exist, but rather:

doubleArray = []

What am I not seeing or what am I forgetting? , I'm sure it's something totally obvious but I don't see it....

Things I have tried:

  • Use comma.

  • Use the system decimal symbol:

    DecimalFormat format=(DecimalFormat) DecimalFormat.getInstance();
DecimalFormatSymbols symbols=format.getDecimalFormatSymbols();
    char sep=symbols.getDecimalSeparator();

  • In the end I have done the different method, but I am still intrigued as to what is happening.

java

2 Answers

  1. Best Answer

    Because in split the string you are passing is a regular expression (regex) and within regular expressions the dot "."has a special meaning. If you want to use it as a point you have to escape it"\\."

    While the method containsdoesn't ask for a regex but a Stringand so it works as expected.

    In java it would look something like this:

    String[] palabras = linea.split("\\.");

    To expand the answer a bit, in regular expressions the dot is a wildcard, which means that it is used to capture any character. You have more info in RegexOne

    • 7

  2. As Luiggi Mendoza mentions, the method split(String regex)receives as a parameter a string that represents a regular expression. Another alternative method to take the point .as a separation character you can apply the following:

    double valor = 8545200054.846546;

String ValorStrExponente = String.valueOf(valor);
String ValorStrCompleto = BigDecimal.valueOf(valor).toPlainString();

String[] PartesValor = ValorStrCompleto.split("[.]");

System.out.println("Valor convertido directo a String: "+ValorStrExponente);
System.out.println("Parte entera: "+PartesValor[0]);
System.out.println("Parte decimal: "+PartesValor[1]);

    If you put the square brackets around the point, it explicitly takes it as a string separation criterion. I also recommend using the method toPlainString(double valor)of the class BigDecimal, since if the value doubleyou are trying to split into parts is very large and you convert it directly with String.valueOf(double valor), it will give you an exponential value as a result. If you run the above code, it generates the following output:

    Valor convertido directo a String: 8.545200054846546E9
Parte entera: 8545200054
Parte decimal: 846546
    • -1