Iterable Immutable List Assignment
Contents
Code To Investigate
Iterable
Iterator
ImmutableList
public interface ImmutableList<E> extends Iterable<E> { E head(); ImmutableList<E> tail(); boolean isEmpty(); }
Code To Implement
DefaultImmutableList
class: | DefaultImmutableList.java | |
methods: | head tail isEmpty iterator |
|
package: | immutable.list.assignment | |
source folder: | src/main/java |
default constructor
constructs a new empty immutable list
DefaultImmutableList()
cons constructor
construct a new immutable list with head and tail
DefaultImmutableList(E head, ImmutableList<E> tail)
head
public E head()
Analogous to the SML List hd method.
tail
public ImmutableList<E> tail()
Analogous to the SML List tl method.
isEmpty
public boolean isEmpty()
Analogous to the SML List null method.
iterator
public Iterator<E> iterator()
Lists
Lists
is a class which holds a number of static methods. As we know, in the Kingdom of Nouns, Verbs must always have an escort.
The first two static methods nil
and cons
will each call a constructor of the DefaultImmutableList
class. The third method brackets
will use nil
and cons
to build up the desired ImmutableList.
class: | Lists.java | |
methods: | nil cons brackets |
|
package: | immutable.list.assignment | |
source folder: | src/main/java |
nil
public static <E> ImmutableList<E> nil()
Analogous to the SML List nil constructor.
Note: often SML programs use empty brackets []
instead of nil
.
cons
public static <E> ImmutableList<E> cons(E head, ImmutableList<E> tail)
Analogous to the SML List :: constructor.
brackets
@SafeVarargs public static <E> ImmutableList<E> brackets(E... elements)
brackets
accepts variable length arguments as specified by the ...
syntax. When implementing the brackets
method you can treat elements
as an array. Combining generics and varargs https://stackoverflow.com/questions/14231037/java-safevarargs-annotation-does-a-standard-or-best-practice-exist can be problematic] if the implementation lets the E[] escape since it will actually be an Object[]. The @SafeVarargs annotation indicates a promise that you will rely only on the elements of the array being of type E and not the array being of type E[]. This should not be a problem since you should not require any unsafe use of varargs.
Note: be sure to cons
the elements on from the back of the elements
array to the front.
Example
class: | ListsExample.java | |
package: | immutable.list.example | |
source folder: | src/main/java |
The code:
ImmutableList<Integer> numbers = Lists.brackets(4, 66, 99); for (int i : numbers) { System.out.println(i); }
produces:
4 66 99
Test
class: | IterableAssignmentTestSuite.java | |
package: | immutable.list.assignment | |
source folder: | src/test/java |