如何在另一个 class 中使用 Boolean 方法检查字符串参数？

Question

I'm working on an a java assignment for school, it's about a phone calling card system, where there are various classes for each type of calling card, I am stuck on part where I use this supplied CallZone class to check if the zone put in the parameter is valid, I am not sure how to call its isValidZone method in the phonecard class, such as SuperNA10Card class.

I am not sure if this the proper way to use the CallZone class to to check if the paramater zone is vaild.

if(zone.equals("canada")){return true;} 
or
if(CallZone.isValidZone(zone) == true){return true}

here is the CallZone class:

public final class CallZone {

     public static boolean isValidZone(String zone) {
         zone = zone.toLowerCase();
         return (zone.equals("canada") ||
             zone.equals("usa") ||
             zone.equals("europe") ||
             zone.equals("asia") ||
             zone.equals("anz") ||
             zone.equals("latinam") ||
             zone.equals("africa")
         );
     }
}

and here is one of the Phonecard classes, SuperNA10 class, using it to check if the zone is valid:

public class SuperNA10 extends PhoneCard{
    final double canMinRate = 0.05;
    final double usMinRate = 0.10;
    final double weeklyMainFee = 0.50;

    public SuperNA10(long no, int passwd){
      super(no, passwd,10.00) //invokes superclass class constructor sets no, passwd and balance to 10.00
    }

    public boolean allowed(String zone){
     if(CallZone.isValidZone(zone) ){
        return true;
      }else{
       return false;
     }


    }

}

I am not sure how to get the CallZone class to check if the parameter in the SuperNA10 class method allowed is valid, also sorry if my question isn't clear or cause confusion, it's my first time posting.

Answer 1

Since you have a specific number of call zones, you can use an enum like this:

public enum CallZone {

    CANADA, USA, EUROPE; //add any number of zones here

    public static boolean isValid(String zone) {
        return Stream.of(values())
                .anyMatch(s -> s.toString().equalsIgnoreCase(zone));
    }
}

You can also look at using CallZone.valueOf(zone) along with catching IllegalArgumentException , instead of using the Stream as above. But I prefer not to use exceptions for non exceptional scenarios.

And then in your SuperNA10 class, you can use it like:

public boolean allowed(String zone) {
    return CallZone.isValid(zone);
}