Are hard-coded STRINGS ever acceptable?

Question

Similar to Is hard-coding literals ever acceptable?, but I\'m specifically thinking of \"magic strings\" here.

On a large project, we have a table of configuration o

Answer 1

In my experience, this kind of issue is masking a deeper problem: failure to do actual OOP and to follow the DRY principle.

In a nutshell, capture the decision at startup time by an appropriate definition for each action inside the if statements, and then throw away both the config_options and the run-time tests.

Details below.

The sample usage was:

if (config_options.value('FOO_ENABLED') == 'Y') ...

which raises the obvious question, "What's going on in the ellipsis?", especially given the following statement:

(Of course, this same option may need to be checked in many places in the system code.)

Let's assume that each of these config_option values really does correspond to a single problem domain (or implementation strategy) concept.

Instead of doing this (repeatedly, in various places throughout the code):

1. Take a string (tag),
2. Find its corresponding other string (value),
3. Test that value as a boolean-equivalent,
4. Based on that test, decide whether to perform some action.

I suggest encapsulating the concept of a "configurable action".

Let's take as an example (obviously just as hypthetical as FOO_ENABLED ... ;-) that your code has to work in either English units or metric units. If METRIC_ENABLED is "true", convert user-entered data from metric to English for internal computation, and convert back prior to displaying results.

Define an interface:

public interface MetricConverter {
    double toInches(double length);
    double toCentimeters(double length);
    double toPounds(double weight);
    double toKilograms(double weight);
}

which identifies in one place all the behavior associated with the concept of METRIC_ENABLED.

Then write concrete implementations of all the ways those behaviors are to be carried out:

public class NullConv implements MetricConverter {
    double toInches(double length) {return length;}
    double toCentimeters(double length) {return length;}
    double toPounds(double weight)  {return weight;}
    double toKilograms(double weight)  {return weight;}
}

and

// lame implementation, just for illustration!!!!
public class MetricConv implements MetricConverter {
    public static final double LBS_PER_KG = 2.2D;
    public static final double CM_PER_IN = 2.54D
    double toInches(double length) {return length * CM_PER_IN;}
    double toCentimeters(double length) {return length / CM_PER_IN;}
    double toPounds(double weight)  {return weight * LBS_PER_KG;}
    double toKilograms(double weight)  {return weight / LBS_PER_KG;}
}

At startup time, instead of loading a bunch of config_options values, initialize a set of configurable actions, as in:

MetricConverter converter = (metricOption()) ? new MetricConv() : new NullConv();

(where the expression metricOption() above is a stand-in for whatever one-time-only check you need to make, including looking at the value of METRIC_ENABLED ;-)

Then, wherever the code would have said:

double length = getLengthFromGui();
if (config_options.value('METRIC_ENABLED') == 'Y') {
    length = length / 2.54D;
}
// do some computation to produce result
// ...
if (config_options.value('METRIC_ENABLED') == 'Y') {
    result = result * 2.54D;
}
displayResultingLengthOnGui(result);

rewrite it as:

double length = converter.toInches(getLengthFromGui());
// do some computation to produce result
// ...
displayResultingLengthOnGui(converter.toCentimeters(result));

Because all of the implementation details related to that one concept are now packaged cleanly, all future maintenance related to METRIC_ENABLED can be done in one place. In addition, the run-time trade-off is a win; the "overhead" of invoking a method is trivial compared with the overhead of fetching a String value from a Map and performing String#equals.

Answer 2

I think there are two different issues here:

• In the current project, the convention of using hard-coded strings is already well established, so all the developers working on the project are familiar with it. It might be a sub-optimal convention for all the reasons that have been listed, but everybody familiar with the code can look at it and instinctively knows what the code is supposed to do. Changing the code so that in certain parts, it uses the "new" functionality will make the code slightly harder to read (because people will have to think and remember what the new convention does) and thus a little harder to maintain. But I would guess that changing over the whole project to the new convention would potentially be prohibitively expensive unless you can quickly script the conversion.
• On a new project, symbolic constants are the way IMO, for all the reasons listed. Especially because anything that makes the compiler catch errors at compile time that would otherwise be caught by a human at run time is a very useful convention to establish.

Answer 3

If I use a string once in the code, I don't generally worry about making it a constant somewhere.

If I use a string twice in the code, I'll consider making it a constant.

If I use a string three times in the code, I'll almost certainly make it a constant.

Answer 4

I too prefer a strongly-typed configuration class if it is used through-out the code. With properly named methods you don't lose any readability. If you need to do conversions from strings to another data type (decimal/float/int), you don't need to repeat the code that does the conversion in multiple places and can cache the result so the conversion only takes place once. You've already got the basis of this in place already so I don't think it would take much to get used to the new way of doing things.

Answer 5

Another thing to consider is intent. If you are on a project that requires localization hard coded strings can be ambiguous. Consider the following:

const string HELLO_WORLD = "Hello world!";
print(HELLO_WORLD);

The programmer's intent is clear. Using a constant implies that this string does not need to be localized. Now look at this example:

print("Hello world!");

Here we aren't so sure. Did the programmer really not want this string to be localized or did the programmer forget about localization while he was writing this code?

Answer 6

I really should use constants and no hard coded literals.

You can say they won't be changed, but you may never know. And it is best to make it a habit. To use symbolic constants.