I need help using enums to get this program working

Question

So this is my first time asking on stackoverflow but i need help with this problem. I have to use enums that includes constructors, methods, and static methods.

So everything in the main was already written and rest I wrote it but I am lost now.

The question is to solve this half written code and have the output. The output is suppose to look like this:

Today's a weekday. 
The abbreviation for MONDAY is M
The abbreviation for MONDAY is T
The abbreviation for MONDAY is W
The abbreviation for MONDAY is R
The abbreviation for MONDAY is F
The abbreviation for MONDAY is S
The abbreviation for MONDAY is Y
SUNDAY
MONDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
SUNDAY
true
true
true
true

My code so far:

import java.util.List;

public class DayOfWeekDriver
{
    public enum DayOfWeek{
        MONDAY("M"), TUESDAY("T"), WEDNESDAY("W"), THURSDAY("R"), FRIDAY("F"), SATURDAY("S"), SUNDAY("S");

        static{
            MONDAY.next = TUESDAY;
            TUESDAY.next = WEDNESDAY;
            WEDNESDAY.next = THURSDAY;
            THURSDAY.next = FRIDAY;
            FRIDAY.next = SATURDAY;
            SATURDAY.next = SUNDAY;
            SUNDAY.next = MONDAY;
        }

        private DayOfWeek next;

        public DayOfWeek nextDay(){
            return next;
        }

        private String abbreviation;

        private String day;

        DayOfWeek(String abbreviation) {
            this.abbreviation = abbreviation;
        }
        public String getAbbreviation() {
            return abbreviation;
        }  

        public String getDays(){
            return day;
        }  
    }

    public char getLetter(){

    }



    public static void main(String[] args)
    {
        DayOfWeek today = DayOfWeek.FRIDAY;

        if (today == DayOfWeek.SATURDAY ||  today == DayOfWeek.SUNDAY)
        {
           System.out.println("Today's a weekend.");
        }
        else
        {
            System.out.println("Today's a weekday.");
        }

        for (DayOfWeek day : DayOfWeek.values())
        {
           System.out.printf("The abbreviation for %s is %c \n",
                             day, day.getLetter());
        }

        for (Character c : "YMWFTRS".toCharArray())
        {
            System.out.println(DayOfWeek.toDayOfWeek(c));
        }

        List<DayOfWeek> list = DayOfWeek.getDays();

        System.out.println(list.get(0) == DayOfWeek.values()[0]);

        System.out.println(DayOfWeek.MONDAY.next() == DayOfWeek.TUESDAY);

        System.out.println(today.next() == DayOfWeek.SATURDAY);

        System.out.println(DayOfWeek.SUNDAY.next() == DayOfWeek.MONDAY);

    }
}

And also if I can get suggestions where to learn more of java that would be great! Thank you.

Answer 1

An enum is a special type of class. Write it as a stand-alone class. It makes the rest of your program easier to maintain, read, and reason about. Since the elements within the enum are constants, use all uppercase names for maximum readability.

public enum Day {
    SUNDAY,
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY;
};

Now that you have a class, you want to add a feature, a "single letter" day representation. You do that for a class by adding an attribute. Enums are both constants and classes, so we will add the "single letter" day representation to the enum by leveraging it's class-like features.

public enum Day {
    SUNDAY,
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY;

    private String shortName;

    public String getShortName() {
        return shortName;
    }
};

But, how do we set this shortName? The answer is that, since enum is a class, we use the constructor. enum constructors exist, but they are constrained. They must be private to prevent new instances from being constructed (a feature of enums).

public enum Day {
    SUNDAY,
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY;

    private String shortName;

    private Day(String abbreviation) {
       shortName = abbreviation;
    }

    public String getShortName() {
        return shortName;
    }
};

Which leads to the last question, how do we declare the value to be passed into the constructor. Well, you do it when you declare the static value, like so

public enum Day {
    SUNDAY("S"),
    MONDAY("M"),
    TUESDAY("T"),
    WEDNESDAY("W"),
    THURSDAY("R"),
    FRIDAY("F"),
    SATURDAY("Y");

    private String shortName;

    private Day(String abbreviation) {
       shortName = abbreviation;
    }

    public String getShortName() {
        return shortName;
    }
};

This places the "single letter" representation within the thing it represents, providing good code locality and ease of maintenance.

To use this in your code

 if ( day == Day.MONDAY ) { // Typical enum comparison

 System.out.println(day.getShortName()); // prints the day's short name

When learning Java, it is difficult to start off with good object-orientation. Your question was basically one of "how to I add something to an enum" but because you used your enum, embedded into another class, it was being solved in the wrong class. You started programming "how can I make this class give me the right answer for that enum". Don't program that way, if you can avoid it. Instead write your code such that the "other object" gives you the answer.

enum in Java is a port of an idea in another language. Java did a great job of both making the enum look like C's enum, and making it behave like an integrated component of the Java language. That said, people initially are exsposed to C's enum syntax, which means they are exposed to C's enum maintenance problems. So, your approach is understandable for a person learning Java and Java's enums. That said, using the enum as an object will make your code faster, easier to read, and easier to reason about. Now that you've seen a different approach, use it when it is appropriate.