Can you pass an enum class to a method (java)

Question

I want to pass a specific enum class to a method. Is this possible? The method would accept any enum. I am trying to create a function that will take a type of enum and make a menu out of it, returning the enum that was selected.

An example enum class

  public enum METHODOFTRANSPORTATION {
        CAR("car"), BUS("bus"), COMMUTTER_RAIL("commuter rail"),MAINMENU("GO TO MAIN MENU");

        private String choice;

        METHODOFTRANSPORTATION(String choice){
            this.choice = choice;
        }

        public String getMethodOfTransportation(){
            return choice;
        }
    }

My Example class implementing the enum

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;


public class Ticket{

    private static HashMap<Integer, Ticket> hm= new HashMap<>();
    private int ticketID = 0;

    private METHODOFTRANSPORTATION methodOfTransportation;

    Ticket(){
        //Call method of Transportation to create ticket
        //GETTING ERROR HERE!
        this.methodOfTransportation = createMethodOfTransportation(METHODOFTRANSPORTATION);
    }

    Ticket(METHODOFTRANSPORTATION methodOfTransportation){
        this.methodOfTransportation = methodOfTransportation;
    }

    public Enum<?> getMethodOfTransportation() {
        return methodOfTransportation;
    }   

    public Enum<?> createMenuChoice(Enum<?> e) {
        System.out.println("**************************");

        Scanner s = new Scanner(System.in);
        int input = 0;
        boolean intFlag = false;
        Enum<?> mot;

        //Validate user input for menu selection
        do{
            //Print our Enums allowed variables
            for(int i=0; i< e.getDeclaringClass().getEnumConstants().length; i++){
                System.out.printf("%d. %s",i,e.getDeclaringClass().getEnumConstants()[i]);
            }

            System.out.println("Please enter a valid menu entry (");
            for(int i = 0; i< e.getDeclaringClass().getEnumConstants().length; i++){
                if(i == e.getDeclaringClass().getEnumConstants().length){
                    System.out.println(i);
                }
                else{
                    System.out.print(i + ",");
                }
            }
            System.out.print("> ");

            if(s.hasNextInt()){
                input = s.nextInt();
                for(int i = 0; i< e.getDeclaringClass().getEnumConstants().length; i++){
                    if(input == i){
                        //*********************************************
                        //HOW DO I RETURN THE CORRESPONDING VALUE HERE?
                        //*******************************************
                        mot =  ;
                    }
                }
            }
            else{
                s.next();
            }
        }
        while(false);

        //WHAT SHOULD I RETURN HERE??
        return METHODOFTRANSPORTATION.CAR;
    }


}

Is this even possible? I just want one method that will take any class of enum, and return the enum value. Is there a better way to do this??

Essentially my driver class would look like

public class Driver {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Ticket t = new Ticket();

        Enum<?> mot = t.getMethodOfTransportation();
        if(mot == METHODOFTRANSPORTATION.CAR){
            //....
        }
        //...

        //OR
        /*
         * switch(mot){
         *      case(METHODOFTRANSPORTATION.CAR): ...
         *      ...
         *      ...
         * }
         */
    }


}

Answer 1

Thank you guys I have found a solution. @BoppreH THANKYOU!!

Ticket.java createMenuChoice method

    //Using introspection
    public Enum<?> createMenuChoice(Class<?> c) {
        //Variables
        int input = -1;
        Enum<?> output = null;
        Scanner s = new Scanner(System.in);

        do{
            //Print Menu
            for(int i = 0; i < c.getEnumConstants().length; i++){
                System.out.printf("%d. %s\n",i+1,c.getEnumConstants()[i].toString());
            }

            //Get Selection
            System.out.println("Please enter a valid menu entry");

            if(s.hasNextInt()){
                input = s.nextInt();
                for(int i = 0; i < c.getEnumConstants().length; i++){
                    if(input == i + 1){
                        return (Enum<?>) c.getEnumConstants()[i];
                    }
                }
            }
            else{
                s.next();
            }
        }while(true);
    }
}

Driver.java I can call this using

MainMenu inputMm = (MainMenu) t.createMenuChoice(MainMenu.class);

and then check for entries with

if(inputMm == MainMenu.BUY_PASS){
} ....

Answer 2

Yes, it is possible. You can declare your method like this:

public <T extends Enum<T>> T doSomething(Class<T> clazz) {
     EnumSet<T> all = EnumSet.allOf(clazz);
     ......
}

Or you can even avoid the whole Class<T> part and just ask for an EnumSet of choices:

public <T extends Enum<T>> T menu(EnumSet<T> options) {
     List<T> lst = new ArrayList(options);
     int idx;
     // display the list and prompt for idx
     return lst.get(idx);
}

And then you would call it as:

METHODOFTRANSPORTATION mot = menu(EnumSet.allOf(METHODOFTRANSPORTATION.class));

And now you don't have to mess around with reflection. Let EnumSet do that for you.

Answer 3

The correct way of referring to a class in Java is ClassName.class. So your line would be:

this.methodOfTransportation = createMethodOfTransportation(METHODOFTRANSPORTATION.class);

METHODOFTRANSPORTATION.class returns a Class-type object. You can then use reflection to inspect its name, possible values, etc. Here is more info on enum reflection.

The name createMethodOfTransportation would not be appropriate though, since it wouldn't have anything to do with the specific enum METHODOFTRANSPORTATION.