Difference of dates with Legend in a Textfield

Question

I am developing a hotel system and would like to automate some features in the system.

I would like that when you select two dates being the dataEntrada and dataSaida using Calendar, make that when choosing these dates, appear the difference of days in a TextField nominee QdtDiaria automatically. It would be possible?

Answer 1

Try this way using the package classes java.time:

 public long subtrairData(Date dataEntrada, Date dataSaida) {

    LocalDateTime LocalDataEntrada = dataEntrada.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
    LocalDateTime LocalDataSaida = dataSaida.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();

    return ChronoUnit.DAYS.between(LocalDataEntrada, LocalDataSaida);
}

Functioning in the IDEONE.

Note: read this article in this reply(credits to @Math by link) a good explanation of why to use the classes in the java.time package for compare dates, not older native classes, such as Date and Calendar.

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UPDATE

And to fill a JTextField with this difference within a button action (as stated in the comments), just make the call of the method cited within the setText() of its component, thus:

myButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        myJTextField.setText(String.valueOf(subtrairData(dataEntrada,dataSaida)));
    }
});

Like the return of the method, even though it’s in days, it’s like long, you need to convert to String, using String.valueOf().

Note: The values of the date fields must be validated before passing them as parameters of the above method, so that they do not arrive empty or invalid dates, thus avoiding the release of exceptions.

References:

Subtract JAVA dates from picking the days difference

Calculate days between two Dates in Java 8

Java 8: Calculate Difference between two Localdatetime

Convert java.util.Date to java.time.Localdate