如何在Java中将char与数字进行比较

Question

I got a problem and I think it is in comparing a char with a number.

String FindCountry = "BB";

Map<String, String> Cont = new HashMap <> ();

Cont.put("BA-BE", "Angola");
Cont.put("9X-92", "Trinidad & Tobago");



for ( String key : Cont.keySet()) {

  if (key.charAt(0) == FindCountry.charAt(0) && FindCountry.charAt(1) >= key.charAt(1) && FindCountry.charAt(1) <= key.charAt(4)) {

    System.out.println("Country: "+ Cont.get(key));

  }
}

In this case the code print "Angola", but if

String FindCountry = "9Z" 

it doesn't print anything. I am not sure I think the problem is in that it can't compare that is '2' greater than 'Z'. In that example, I got only two Cont.put(), but in my file, I got much more and a lot of them are not only with chars. I got a problem with them.

What is the smartest and best way to compare char with a number ? Actually, if I set a rule like "1" is greater than "Z" it will be okay because I need this way of greater: AZ-9-0.

Thanks!

Answer 1

You can use a lookup "table", I used a String :

private static final String LOOKUP = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

And then compare the chars with indexOf() , but it seems messy and could probably be achieved more easily, I just can't come up with something easier at the moment:

String FindCountry = "9Z";

Map<String, String> Cont = new HashMap<>();

Cont.put("BA-BE", "Angola");
Cont.put("9X-92", "Trinidad & Tobago");

for (String key : Cont.keySet()) {
    if (LOOKUP.indexOf(key.charAt(0)) == LOOKUP.indexOf(FindCountry.charAt(0)) &&
        LOOKUP.indexOf(FindCountry.charAt(1)) >= LOOKUP.indexOf(key.charAt(1)) &&
        LOOKUP.indexOf(FindCountry.charAt(1)) <= LOOKUP.indexOf(key.charAt(4))) {
        System.out.println("Country: " + Cont.get(key));
    }
}

Answer 2

If you only use the characters AZ and 0-9 , you could add a conversion method in between which will increase the values of the 0-9 characters so they'll be after AZ :

int applyCharOrder(char c){
  // If the character is a digit:
  if(c < 58){
    // Add 43 to put it after the 'Z' in terms of decimal unicode value:
    return c + 43;
  }
  // If it's an uppercase letter instead: simply return it as is
  return c;
}

Which can be used like this:

if(applyCharOrder(key.charAt(0)) == applyCharOrder(findCountry.charAt(0))
    && applyCharOrder(findCountry.charAt(1)) >= applyCharOrder(key.charAt(1))
    && applyCharOrder(findCountry.charAt(1)) <= applyCharOrder(key.charAt(4))){
  System.out.println("Country: "+ cont.get(key));
}

Try it online.

Note: Here is a table with the decimal unicode values. Characters '0'-'9' will have the values 48-57 and 'A'-'Z' will have the values 65-90 . So the < 58 is used to check if it's a digit-character, and the + 43 will increase the 48-57 to 91-100 , putting their values above the 'A'-'Z' so your <= and >= checks will work as you'd want them to.

---

Alternatively, you could create a look-up String and use its index for the order:

int applyCharOrder(char c){
  return "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".indexOf(c);
}

Try it online.

PS: As mentioned in the first comment by @Stultuske , variables are usually in camelCase, so they aren't starting with an uppercase letter.

Answer 3

As the others stated in the comments, such mathematical comparison operations on characters are based on the actual ASCII values of each char. So I'd suggest you refactor your logic using the ASCII table as reference.