This package contains classes related to creating immutable collections,
particularly an immutable list. The java.util package already contains
unmodifiable wrapper objects for all of its collection classes but these have
two problems. First, they cannot remove the mutator methods present in the
collection interfaces themselves. This means that, for example, the
Collection.add()
method is present even though it must not be
called at runtime. Second, they do not support operations that work on
collections as a whole such as applying an operation or searching for an
item.