Limit a country code string to 2 characters

Question

I would like to declare a String for a country variable in Java which would only take 2 characters such as IN, DE etc. I am a bit confused so can someone please help me?

If I try to assign a value something like this then it should work: country = "IN" but if I try to assign a value country = "IND" then it should throw an error.

I am a bit familiar with regex but wanted to confirm if there is any built-in String method that would do this.

public class App {
    public static void main(String[] args) {
        String country = "";
        //char[] array = new char[2];
        //String country = new String(array); 
        // String[] country = new String[2];

    }
}

Answer 1

The simple answer is: you can't.

The String class doesn't have any means that allow you to restrict its objects on assignment. There is no way in Java to get

String someString = "INx":

to fail. This means, you are left with two choices:

• validation: this means you have utility methods (for example using regular expressions) that check arbitrary string objects and that then tell you whether that string is a valid country abbreviation, like: String countryCode = validate("INx")
• creating an explicit type

For the later, you would probably look at creating your own enum implementation that simply lists all the valid codes you care about. Or you pick up some existing library.

Answer 2

Not possible, but:

It is good style for values with some business relevance to create classes for them.

A class Country, some usage as:

Country bulgaria = new Country("BG");


public class Country {
   String code;
   public Country(String code) {
       if (code.length() > 2) {
           throw new IllegalArgumentException("At most 2 chars: " + code);
       }
       this.code = code;
   }

If language comes into the picture use Locale.

Answer 3

For a solid solution, I agree with @GhostCat, you can use Locale to get the countries iso codes and you can check if your code exist or not in this list:

final Set<String> isoCountries = Set.of(Locale.getISOCountries());

String country = "DZ";
if (!isoCountries.contains(country.toUpperCase())) {
    throw new IllegalArgumentException(country + " country code not valid.");
}

Answer 4

for this manner, you can use Regular Expressions here! and Test the expression using! Here is my solution

import java.util.Scanner;

public class StringChecker {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Please enter 2 char String: ");
        String str = scanner.next();
        String str_valid = "";
        if (str.matches("^[a-zA-Z0-9]{2}$")){
            str_valid = str;
            System.out.println(str_valid);
        }else{
            System.out.println("String is not in 2 chars");
        }

    }
}

Answer 5

It's not possible as you expecting but you can create validation for that,

String country = sc.next();
if(country.length() == 2){
    //do something 
}else{
    // do something
}

To ask for the string of length = 2 until it gets.

boolean flag = true;
while(flag){
    String country = sc.next();
    if(country.length() == 2){
        flag = false;
        //do something 
    }else{
        // do something
    }
}

Answer 6

Make country a private instance variable and create a setter method, in which you can do validations.

P.S. The following is horrible code. But, I hope it'd help you get the idea.

package com.company;

public class Main {

private static String country = "";
public static void main(String[] args) throws Exception {

    Main m = new Main();
    m.setCountry("DEX");
    System.out.println(country);
}

public void setCountry(String country) throws Exception {

    if(this.country.length() != 0){

        throw new Exception("The country is already set");
    }

    else if (country.length() != 2) {

        throw new Exception("The country string's size cannot be greater than 2");
    }
    else {
        this.country = country;
    }
}
}