how to store date in particular format if input itself is a date?

Question

I am trying to store the expiry date in exp. The format I want to store it is "yyyy-MM-dd".I tried using SimpleDateFormat and than tried to format to get a string and than parse the string as follows:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date exp = sdf.parse(sdf.format(c.getTime()));

But result is I don't get date saved in exp as yyyy-MM-dd. I want to know given a date in particular format How do I convert it in other date format if the input itself is a date in one format and output is date is other format. I have used GregorianCalendar to getTime.

The format of manufacturing date is"yyyy-MM-dd"; I want the date to be stored in same format in exp;

public void calculateExpiryDate(List <Item> items) {
    Iterator <Item> itr = items.iterator();

    while (itr.hasNext()) {
        Item i = itr.next();
        Date md = i.getManufacturingDate();
        int ubm = i.getUseBeforeMonths();

        Calendar c = new GregorianCalendar();
        c.setTime(md);
        //System.out.println(c);
        c.add(Calendar.MONTH, ubm);

        Date exp = c.getTime();
        i.setExpiryDate(exp);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(md + " " + ubm + " " + sdf.format(exp) + "  " + " " + i.getId());
    }
}

here is my code for Items:

public class Item implements Comparable<Item>{
    private int id;
    private String description;
    private float weight;
    private float price;
    private Date manufacturingDate;
    private int useBeforeMonths;
    private Date   expiryDate;


    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public float getWeight() {
        return weight;
    }
    public void setWeight(float weight) {
        this.weight = weight;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    public Date getManufacturingDate() {
        return manufacturingDate;
    }
    public void setManufacturingDate(Date manufacturingDate) {
        this.manufacturingDate = manufacturingDate;
    }
    public int getUseBeforeMonths() {
        return useBeforeMonths;
    }
    public void setUseBeforeMonths(int useBeforeMonths) {
        this.useBeforeMonths = useBeforeMonths;
    }

    public void setExpiryDate(Date expiryDate) {
        this.expiryDate = expiryDate;
    }
    public Date getExpiryDate() {
        return expiryDate;
    }
    @Override
    public int compareTo(Item arg0)
    {
        Date exp1=getExpiryDate();
        Date exp2=arg0.getExpiryDate();
        if(exp1.getYear()==exp2.getYear())
        {
            if(exp1.getMonth()==exp2.getMonth())
            {
                return exp2.getDate()-exp1.getDate();
            }
            else
                return exp2.getMonth()-exp1.getMonth();
        }
        return exp2.getYear()-exp1.getYear();
    }   

} 

Answer 1

If I understand correctly...

You want, inside setExpiryDate get the date as a String into the format "yyyy-MM-dd". And as a constraint, the Item.setExpiryDate doesn't want to care about any SimpleDateFormat.

A solution is to use a kind of decorator pattern to redefine the string representation of a date.

public final class ExpirationDate extends Date {
    private final SimpleDateFormat formatter;

    public ExpirationDate(Date origin) {
        super(origin.getTime());
        this.formatter = new SimpleDateFormat("yyyy-MM-dd");
    }

    @Override
    public final String toString() {
        return formatter.format(this);
    }
}

And wrap your Date in a ExpirationDate every time you need this kind of representation:

Date exp = c.getTime();
i.setExpiryDate(new ExpirationDate(exp));

Answer 2

Try this -

import java.util.Date;
import java.util.GregorianCalendar;
import java.text.SimpleDateFormat;
import java.text.DateFormat;
import java.util.Calendar;

public class Temp {
  public static void main(String args[]) {
      String startDateString = "2012-03-12";
      DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
      Date startDate;
      try{
          startDate = df.parse(startDateString);

          Calendar c= new GregorianCalendar();
          c.setTime(startDate);
          c.add(Calendar.MONTH, 3);
          Date exp=c.getTime();
          SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
          String expDate = sdf.format(exp).toString();
          System.out.println(expDate);
      }catch(Exception e){
      }
  }//Body
}

Answer 3

I am not sure if you manufacturing date is displayed in SDF format you mentioned. The SDF format can be used for storing date in String format

Calendar c = Calendar.getInstance();
    Date md = new Date();
    int ubm = 4;
    //System.out.println(c);
    c.setTime(md);
    c.add(Calendar.MONTH, ubm);

    Date exp = c.getTime();
    //i.setExpiryDate(exp);
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    String strExpiry =  sdf.format(exp);
    System.out.println("Expiry Date in String format " + strExpiry );
    Date dtExpiry = sdf.parse(strExpiry);
    System.out.println("Expiry Date in Date format " + dtExpiry);

where as if converted to Date the result will be again the complete Date output as shown below

Expiry Date in String format 2016-02-01
Expiry Date in Date format Mon Feb 01 00:00:00 IST 2016