Best way to concatenate List of String objects? [duplicate]

Answer 1

If you are developing for Android, there is TextUtils.join provided by the SDK.

Answer 2

In java 8 you can also use a reducer, something like:

public static String join(List<String> strings, String joinStr) {
    return strings.stream().reduce("", (prev, cur) -> prev += (cur + joinStr));
}

Answer 3

Your approach is dependent on Java's ArrayList#toString() implementation.

While the implementation is documented in the Java API and very unlikely to change, there's a chance it could. It's far more reliable to implement this yourself (loops, StringBuilders, recursion whatever you like better).

Sure this approach may seem "neater" or more "too sweet" or "money" but it is, in my opinion, a worse approach.

Answer 4

I somehow found this to be neater than using the StringBuilder/StringBuffer approach.

I guess it depends on what approach you took.

The AbstractCollection#toString() method simply iterates over all the elements and appends them to a StringBuilder. So your method may be saving a few lines of code but at the cost of extra String manipulation. Whether that tradeoff is a good one is up to you.

Answer 5

Depending on the need for performance and amount of elements to be added, this might be an ok solution. If the amount of elements are high, the Arraylists reallocation of memory might be a bit slower than StringBuilder.

Answer 6

Using the Functional Java library, import these:

import static fj.pre.Monoid.stringMonoid;
import static fj.data.List.list;
import fj.data.List;

... then you can do this:

List<String> ss = list("foo", "bar", "baz");
String s = stringMonoid.join(ss, ", ");

Or, the generic way, if you don't have a list of Strings:

public static <A> String showList(List<A> l, Show<A> s) {
  return stringMonoid.join(l.map(s.showS_()), ", ");
}