In his Disturbing Thoughts from a Developing Mind blog, fellow kiwi Mark Derricutt discusses a situation where new for loops don't provide enough power for a particular case. (And yes this blog has been sitting drafted but unpublished for ages :( )

The case in point is building a String from the concatenation of a List of Strings with some separator between them, in this case a semi-colon.

The problem is expressed as "append the separator after each element, except the last one". What seems to have evaded Mark and his commenters is that the problem can be expressed differently.

If you restate the problem as "append the separator before each item except the first one" then you are one step away from what seems to me to be an elegant solution, at least compared to the others offered.

That final step is to realise that "except the first one" can be rephrased as except the first one in which case you prepend nothing".

Applying this to the relevant section of Mark's code yields

StringBuilder sb = new StringBuilder();
String separator = "";
for (String listenerClassName : data.TEST_LISTENERS) {
    if (listenerClassName != null && !"".equals(listenerClassName)) {
        sb.append(separator).append(listenerClassName);
        separator = ";";
    }
}

There is a more OOish solution, which is to have a (tiny) class thus

public Class Separator {
    private String next = "";
    private String separator;
    public Separator(String separator) {
        this.separator = separator;
    }

    public String get() {
        String result = next;
        next = separator;
        return result;
    }
}

which returns an empty string the first time get() is called, then the configured value thereafter.

With this we can code the loop as

StringBuilder sb = new StringBuilder();
Separator sep = new Separator(";");
for (String listenerClassName : data.TEST_LISTENERS) {
    if (listenerClassName != null && !"".equals(listenerClassName)) {
        sb.append(sep.get()).append(listenerClassName);
    }
}

So how do you tackle this problem?