Assign enum values based on value parameter in JAVA

Question

I have a card class:

public class Card{        
    private final Rank rank;
    public Rank rank() { return rank; }
    public Card(Rank rank) {
        this.rank = rank;
    }    
}

Where Rank is an enum defined as so:

enum Rank {
    TWO ("2"),
    THREE ("3"),
    FOUR ("4"),
    private final String rankNum;
    private Rank(String rankNum) { this.rankNum = rankNum; }
    public String rankNum(){ return rankNum; }
}

So my goal is to input a string "2" as a command line argument and then make a new card object with its rank value as TWO. If the input were "TWO" then it would be possible to do this but I do not know how to do it if the input is "2".

If the input were "TWO" I would do the following:

Card firstCard = new Card(Rank.args[0]);

I hope this question wasn't too badly phrased or obvious, as you can tell I'm still in my early stages, but I've searched this question for hours to no avail.

Answer 1

If your expected input is "2" (as opposed to "TWO" ), you could add a utility static method in your enum.

Something in the lines of:

public static Rank forValue(String value) {
    // null/empty check
    if (value == null || value.isEmpty()) {
        throw new IllegalArgumentException();
    }
    // iterates enum values
    for (Rank r : Rank.values()) {
        // found a match
        if (r.rankNum().equals(value)) {
            return r;
        }
    }
    // iteration over, no match found
    throw new NoSuchElementException();
}

Answer 2

You can't do that. You should check if your command line argument is equals to any Rank value, and then create your new Card

Answer 3

Use Rank.lookupByNumber("2") to get Rank.TWO

import java.util.HashMap;

enum Rank {
    TWO("2"), THREE("3"), FOUR("4");

    private static final HashMap<String, Rank> lookupTable = new HashMap<>();

    static {
        for (Rank rank : Rank.values()) {
            lookupTable.put(rank.rankNum, rank);
        }
    }

    private final String rankNum;

    private Rank(String rankNum) {
        this.rankNum = rankNum;
    }

    public String rankNum() {
        return rankNum;
    }

    public static Rank lookupByNumber(String number) {
        return lookupByNumber(number);
    }
}

In a static block you initialize a lookupTable with the strings you provide as keys. So you can very easily and very quickly grab the Rank enum by the String provided

Answer 4

There is no other way then loop through the values of your Enum , and check if your given value matches with any value in the Enum constants.

String value = //given value Ex: "2"
for (Rank rank : Rank.values()) {
        if (rank.rankNum().equals(value)) {
            return rank;
        }
}

Answer 5

What about this

public enum Rank {

    TWO ("2"),
    THREE ("3"),
    FOUR ("4");

    private String description;

    private Rank(final String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    @Override
    public String toString() {
        return this.description;
    }

Main:

public static void main( String[] args ) throws Exception {

    if(args.length > 0) {
        String rank = args[0].trim();
        if (rank.equals(Rank.TWO.toString())) {
            System.out.println("entered rank is: " + Rank.TWO.getDescription());
        }
    }
}