Advancing Dates with Local Date

Question

I’m trying to make the date the user enters in the constructor advanced in 1 day.

However I am not getting the expected result, is being returned the same day. I tried to check by debug and simply the plusDays() not sum 1 day. I’m probably doing something wrong, can help me?

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class Data {
    private Integer dia;
    private Integer mes;
    private Integer ano;

    private LocalDate dataHoje;


    public Data(Integer dia, Integer mes, Integer ano) {

        if(dia > 31 || dia <= 0) {
            throw new RuntimeException("Não existem dias nulos, nem dias maiores que 31!");

        } else {
            setDia(dia);
        }

        if (mes > 12) {
            throw new RuntimeException("Só existem 12 meses!");

        } else if (mes <= 0) {
            throw new RuntimeException("Não podem existir meses negativos ou nulos!");

        }else {
            setMes(mes);
        }


        if(ano < 0) {
            throw new RuntimeException("Não trabalhamos com anos A.C! Insira um D.C");  
        } else {            
            setAno(ano);
        }

        this.dataHoje = LocalDate.of(ano, mes, dia);
    }


    public Data() {
        LocalDate now = LocalDate.now();
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        System.out.println("A Data de hoje é : " + now.format(formatter));
    }


    public String getDataInserida() {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        return dataHoje.format(formatter);
    }



    public LocalDate avancarDia() {
        dataHoje.plusDays(1);
        return dataHoje;
    }
// aqui em baixo ficam os getters e setters dos atributos primitivos

}

This is my app class.

public class App {
    public static void main(String[] args) {
        Data dataSistema = new Data();
        Data data = new Data(8,12,1998);

        System.out.println(data.getDataInserida());

        data.avancarDia();

        System.out.println(data.getDataInserida());
    }
}

Answer 1

The classes of java.time sane immutable, and methods such as plusDays return another instance with the modified values. That is, if you just do:

dataHoje.plusDays(1);

The return of the method is ignored (as it is not assigned to any variable), and dataHoje continues with the same original value.

Then you should do:

public LocalDate avancarDia() {
    dataHoje = dataHoje.plusDays(1);
    return dataHoje;
}

With this, the value of dataHoje is updated to the next day.

Answer 2

Hello,

Try it this way

    LocalDate hoje = LocalDate.now();
    LocalDate amanha = hoje.plusDays(1);
    System.out.println(amanha);