How can I can take in a valid date as a string but if not keep the default assigned byt the default constructor?

Question

I'm trying to create a calendar class in which I initial a default date. When a user creates the class the default Constructor is assigning the value "01-01-2012". If the user enters a valid date as a string parameter the second constructor will assign the new date.If not I would like the class to give a friendly warning this is not a valid date and go ahead and keep the default assignment.( eg. If the user enter "02/31/2012". This would throw the warning and go ahead and create the instance while setting the default to "01-01-2021".) I also created a method to set the date so this can be changed later once they give a valid date. How should i the second constructor in order to do this? Or is there a better more efficient process in order to do this?

import java.time.*;
import java.time.format.DateTimeFormatter;



public class CalendarDate {

    private String date;
    private DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMMM dd uuuu");
  
    //constructor sets date to January 1, 2012
    CalendarDate(){

       date = "01-01-2012";
    };

    /**
     *  Initializes object's chosen date
     * 
     * @param day - initializes day
     * @param month - initialazes month
     * @param year - initialazes year
     */
    public CalendarDate(String date){

        this.date = date;

    } // 1 - parameter Constructor


    /**
     * 
     *  Sets new date given to this object
     * 
     * @param date sets new date to object
     */
    public void setDate(String date){

        this.date = date;
    }

    /**
     * 
     * Returns objects set date.
     * 
     * @return Returns set date.
     */
    public String getDate(){

        LocalDate getDate = LocalDate.parse(date);
        String formattedDate = getDate.format(formatter);
        return formattedDate;
    }

    /**
     * 
     * Returns object's date
     * 
     * @return Returns object's date
     */
    public String getNextDate(){

        LocalDate dateTime = LocalDate.parse(date);
        LocalDate returnValue = dateTime.plusDays(1);
        String newNextDate = formatter.format(returnValue);
        return newNextDate;
     
    }

    /**
     *  Returns prior date from the object's given date.
     * 
     * @return
     */
    public String getPriorDate(){

        return " ";
    
    }

    /**
     *  Returns the day of the week from the object's given date.
     * 
     * @return
     */
    public String getDayOfWeek(){

        return " ";
    
    }



}


public class Calendar extends CalendarDate{

    public static void main(String[] args){

        CalendarDate testDate = new CalendarDate("06-07-1992");

       testDate.getDate();
        

    }
}

This is what I have so far and I'm wanting to use LocalDate and DateTimeFormatter. Anything will help.

Answer 1

The format specified in the DateTimeFormatter must match the input string e.g.

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        String strDate = "01-01-2012";
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd-MM-uuuu", Locale.ENGLISH);
        LocalDate date = LocalDate.parse(strDate, dtf);
        System.out.println(date);

        // Output in a custom format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMM dd uuuu", Locale.ENGLISH);
        String formatted = formatter.format(date);
        System.out.println(formatted);
    }
}

Output:

2012-01-01
January 01 2012

ONLINE DEMO

Learn more about the modern Date-Time API^* from Trail: Date Time.

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^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}