More efficient way to do if/else branch with variable assignment in Java

Question

The variable "varOptions" is attained via scanner. Basically, I want: [A, B, C, D, E, F] to become: [0, 1, 2, 3, 4, 5]. It is also very important that the code remain non-case sensitive. Currently, this code is rather bulky. I'm wondering if there is a way to make this more efficient?

    if ("A".equalsIgnoreCase(varOptions)) {
        int varOpt = 0;
    } else if ("B".equalsIgnoreCase(varOptions)) {
        int varOpt = 1;
    } else if ("C".equalsIgnoreCase(varOptions)) {
        int varOpt = 2;
    } else if ("D".equalsIgnoreCase(varOptions)) {
        int varOpt = 3;
    } else if ("E".equalsIgnoreCase(varOptions)) {
        int varOpt = 4;
    } else if ("F".equalsIgnoreCase(varOptions)) {
        int varOpt = 5;
    }

Is this only for those specific values? What happens with "G"? Furthermore, this sounds like a question more appropriate for Code Review than SO. — chrylis -cautiouslyoptimistic-, Jul 12 '16 at 23:49
What happens if input is other than A-F, or is that not going to happen? — Bohemian, Jul 13 '16 at 00:12

Matt Coats · Answer 1 · 2016-07-13T00:01:09.467

Convert the varOptions variable to a character if it is not already (as opposed to a string). Once it's a character, you can cast it to an integer, which will convert the character to its ASCII code. The 'A' character has an ASCII code of 65. B is 66. C is 67, etc. etc.

To remain case insensitive, convert the character to uppercase before converting to an integer.

Therefore, after casting it to an integer, you just subtract 65, and you will have a number between 0 and 5:

int varOpt = (int)Character.toUppercase(varOptions);
varOpt -= 65;

The code above assumed varOptions is already of type char. Note that the case to an int is not required, but improved readability. One could just as easily do:

int varOpt = Character.toUppercase(varOptions);

Full code example, assuming varOptions is a string:

char varOptChar = varOptions.charAt(0); // grab first character
int varOpt = (int)Character.toUppercase(varOptChar);
varOpt = varOpt - 65;

varOpt should now be between 0 and 5 for your example. To understand this you need to understand that characters have decimal representations in a computer. The computer only sees the number 65, but knows that this number indicates an uppercase A. 65 is called an ASCII code; you can find a table of ASCII codes here: http://www.asciitable.com/

Could you give me a code example of what you're saying? Sorry. I'm not very familiar with Java syntax. — Jonathan Mousley, Jul 12 '16 at 23:55
@JonathanMousley Added! The code itself is not complex, but if you're unfamiliar with ASCII codes I can see how this might be confusing. I tried to add a short little explanation. — Matt Coats, Jul 13 '16 at 00:02
Instead of writing `- 65` I would suggest `- 'A'` so that you don't need an ASCII table to understand the code. — assylias, Jul 13 '16 at 02:29

score 0 · Answer 2 · 2016-07-13T10:10:38.060

int varOpt = Character.toUppercase( varOptions.charAt(0) ) - 'A'; // assuming varOptions is String

or

int varOpt = Character.toUppercase( varOptions ) - 'A'; // assuming varOptions is char

You can also use switch on String:

int varOpt;
switch( varOptions.toUpperCase() ) {
    case "A":
        varOpt = 0; break;
    case "B":
        varOpt = 1; break;
    // etc
}

or use a Map, if you intend to do something else than simple char-to-int mapping over a continuous range.

score 0 · Answer 3 · answered Jul 13 '16 at 00:14

0

How about:

int varOpt = " ABCDEF".indexOf(varOptions.toUpperCase());

answered Jul 13 '16 at 00:14

Bohemian

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score -1 · Answer 4 · answered Jul 12 '16 at 23:52

-1

Its not that pretty, but you could do something like this

Map<String, Integer> map = new HashMap<String, Integer>()
{{
   put("A", 1);
   put("B", 2);
   put("C", 3);
   put("D", 4);
   put("E", 5);
   put("F", 6);
}};

// varOpt will be null if it is not in the map
int varOpt = map.get(varOptions.toUpperCase());

answered Jul 12 '16 at 23:52

user1875195

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I have never seen that double curly bracket notation. Does that create an anonymous subclass of HashMap which has an additional static initializer? – Teto Jul 13 '16 at 00:12
@Teto yup. it's also generally discouraged for a couple of reasons - https://blog.jooq.org/2014/12/08/dont-be-clever-the-double-curly-braces-anti-pattern/ https://blog.nishtahir.com/2015/09/27/why-you-shouldnt-use-the-double-brace-initializer/ http://stackoverflow.com/questions/1958636/what-is-double-brace-initialization-in-java http://stackoverflow.com/questions/924285/efficiency-of-java-double-brace-initialization - *"every time you use DBI, a kitten get killed"* – Jul 13 '16 at 10:13

score -1 · Answer 5 · answered Jul 13 '16 at 02:24

-1

An alternative is to parse the letter as an hexadecimal number and subtract 11:

int varOpt = Integer.parseInt(varOptions, 16) - 0xA;

answered Jul 13 '16 at 02:24

assylias

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More efficient way to do if/else branch with variable assignment in Java

5 Answers5