Java Date Utils exercise

Question

I'm doing a training course at the moment and it's causing me a lot of problems. The code is below. The problem I'm having is that the training course requires a specific solution based on the java.time.LocalDate import.

I've tried multiple different avenues to solve this, but the inbuild compiler keeps blowing up. This is my first attempt at learning Java and it's definitely not helping. Code needs to be added at the 3 points specified.

Feels like failure to have to ask for help on this, but I'm unable to see any solution here.

import java.time.LocalDate;

public class ChallengeThree {
    public static String dayOfWeek(String date) {
        /**
         * Returns a String storing the day of the week in all capital letters of the
         * given date String
         * Complete the implementation of the DateUtil class and use it in this function 
         * Arguments
         * date - a String storing a local date, such as "2000-01-01" 
         * Examples
         * dayOfWeek("2000-01-01") returns "SATURDAY"
         */

        // ====================================
        // Do not change the code before this

        // CODE1: Write code to return the day of the week of the String date
        //        using the DateUtil class at the bottom of this file
        

        // ====================================
        // Do not change the code after this
    }

    public static void main(String[] args) {
        String theDayOfWeek = dayOfWeek("2000-01-01");
        String expected = "SATURDAY";
        // Expected output is 
        // true
        System.out.println(theDayOfWeek == expected);
    }
}

class DateUtil {
    LocalDate theDate;

    public DateUtil(String date) {
        /**
         * Initialize the theDate field using the String date argument
         * Arguments
         * date - a String storing a local date, such as "2000-01-01" 
         */

        // ====================================
        // Do not change the code before this

        // CODE2: Write code to initialize the date field of the class
        

        // ====================================
        // Do not change the code after this
    }

    public String dayOfWeek() {
        /**
         * Return a String the day of the week represented by theDate
         */

        // ====================================
        // Do not change the code before this

        // CODE3: Write code to return the String day of the week of theDate
        

        // ====================================
        // Do not change the code after this
    }
}

Answer 1

Use LocalDate.parse to parse the date string into a LocalDate instance and then use LocalDate#getDayOfWeek to get day of week from the LocalDate instance.

public static String dayOfWeek(String date) {
    return LocalDate.parse(date).getDayOfWeek().toString();
}

Also, use String#equals to compare the strings i.e. you should write:

System.out.println(expected.equals(theDayOfWeek));

Note that == compares the references, not the content.

[Update]

This is how you can utilize your DateUtil class to do it.

import java.time.LocalDate;

public class ChallengeThree {
    public static String dayOfWeek(String date) {
        return new DateUtil(date).dayOfWeek();
    }

    public static void main(String[] args) {
        String theDayOfWeek = dayOfWeek("2000-01-01");
        String expected = "SATURDAY";
        System.out.println(expected.equals(theDayOfWeek));
    }
}

class DateUtil {
    LocalDate theDate;

    public DateUtil(String date) {
        theDate = LocalDate.parse(date);
    }

    public String dayOfWeek() {
        return theDate.getDayOfWeek().toString();
    }
}

Answer 2

tl;dr

    LocalDate                          // Represent a date-only, without time-of-day and without time zone.
    .parse( "2000-01-01" )             // Automatically parse a string in standard ISO 8601 format.
    .getDayOfWeek()                    // Returns `DayOfWeek` enum object.
    .equals( DayOfWeek.SATURDAY )      // Comparing `DayOfWeek` objects, returning a `boolean`. 

See this code run live at IdeOne.com.

true

DayOfWeek

The accepted Answer by Avinash is correct, and directly addresses your specific exercise.

But I want to point out that Java offers specific classes to help you with this work.

Specifically, Java offers the DayOfWeek enum class. See Oracle tutorial on enums if you are new to that. You can ask a LocalDate for the enum object representing its day-of-week: LocalDate::getDayOfWeek.

Use smart objects rather than dumb strings. So this code:

String theDayOfWeek = dayOfWeek("2000-01-01");
String expected = "SATURDAY";
System.out.println(theDayOfWeek == expected);

…should be:

LocalDate ld = LocalDate.parse( "2000-01-01" ) ;  // Standard ISO 8601 format is YYYY-MM-DD. 
DayOfWeek dow = ld.getDayOfWeek() ;
DayOfWeek expectedDow = DayOfWeek.SATURDAY ; 
boolean isExpected = dow.equals( expectedDow ) ;

In real work, I would nest that call to LocalDate.parse in a try-catch to trap for the DateTimeParseException in case of faulty input string.

Or make that a one-liner (not that I recommend doing so).

if( 
    LocalDate                          // Represent a date-only, without time-of-day and without time zone.
    .parse( "2000-01-01" )             // Automatically parse a string in standard ISO 8601 format.
    .getDayOfWeek()                    // Returns `DayOfWeek` enum object.
    .equals( DayOfWeek.SATURDAY )      // Comparing `DayOfWeek` objects, returning a `boolean`. 
) { … }

See this code run live at IdeOne.com.

true

By the way, we can get the name of the day localized.

String output = 
    DayOfWeek.SATURDAY
    .getDisplayName​(
        TextStyle.FULL , 
        Locale.CANADA_FRENCH
    )
;
System.out.println( output ) ;

samedi