A repeated string formatting operation

Question

As I'm reading the Java code of some other people, I found him using an approach of assigning a format string to a variable and using the variable for String.format in the code:

private final static String URI_SUFFIX_FORMAT = "view/%s";

@Inject
private UriBuilder uriBuilder;

public void buildUriForMusic(String dir)
{
    ...
    String ret = uriBuilder.buildContentUri(dir, String.format(URI_SUFFIX_FORMAT, "music"));
    ...
}

public void buildUriForBook(String dir)
{
    ...
    String ret = uriBuilder.buildContentUri(dir, String.format(URI_SUFFIX_FORMAT, "book"));
    ...
}

I don't like the use of URI_SUFFIX_FORMAT in the above code because I cannot tell what that String.format is trying to compose and if the number of Strings passed in is correct or not.

I prefer to do this instead:

private String formatUriWithSuffix(String dir, String service)
{
    return uriBuilder.buildContentUri(dir, String.format("view/%s", service));
}

public void buildUriForMusic(String dir)
{
    ...
    String ret = formatUriWithSuffix(dir, "music");
    ...
}

public void buildUriForBook(String dir)
{
    ...
    String ret = formatUriWithSuffix(dir, "book");
    ...
}

What do you think? Which one is better, for what reasons? Do you have a better approach?

Answer 1

Sure, your method is better. It's a pretty straightforward example of some fundamental programming and design concepts:

• You spotted repetition. The same information is being stated multiple times. In this case, the information is how to perform a particular operation for formatting a string. Generally, you should not repeat yourself.
• This clued you in to an abstraction: the implementation of this formatting operation can be abstracted out behind a meaningful name
• With this knowledge you abstracted out the operation by applying an extract method refactoring.
• As a result, you now have code which is:
  • More readable, since the methods are simpler, and the name of the formatting method explains exactly what its purpose is.
  • More maintainable, since now any change to this formatting operation just has one place to occur, rather than having to be made in all the places that it's repeated