guava/src/com/google/common/base/Joiner.java
public final String join(@Nullable Object first, @Nullable Object second, Object... rest) {
    return join(iterable(first, second, rest));
  }
public final String join(@Nullable Object first, @Nullable Object second, Object... rest) {
    return join(iterable(first, second, rest));
  }
Returns a string containing the string representation of each argument, using the previously
configured separator between each.