/*******************************************************************************
* Companion code for the book "Introduction to Software Design with Java",
* 2nd edition by Martin P. Robillard.
*
* Copyright (C) 2022 by Martin P. Robillard
*
* This code is licensed under a Creative Commons
* Attribution-NonCommercial-NoDerivatives 4.0 International License.
*
* See http://creativecommons.org/licenses/by-nc-nd/4.0/
*
*******************************************************************************/
package e2.chapter9;
import java.util.List;
import java.util.Optional;
/**
* See section 9.5.
*
*/
public interface {
/**
* Select an instance of Card from pCards.
*
* @param pCards
* list of cards to choose from.
* @pre pCards != null && !pCards.isEmpty()
* @post If RETURN.isPresent(), pCards.contains(RETURN.get())
*/
Optional<Card> select(List<Card> pCards);
static Optional<Card> first(List<Card> pCards) {
return Optional.of(pCards.get(0));
}
static Optional<Card> lowestBlackCard(List<Card> pCards) {
return null; // This is a stub
}
static Optional<Card> highestFaceCard(List<Card> pCards) {
return null; // This is a stub
}
}This functional interface fulfills a role similar to Function<List<Card>, Optional<Card>>.
However, defining a new, more specific interface makes its intent clearer in the code.
The custom interface provides several benefits:
first, lowestBlackCard, and highestFaceCard.This functional interface fulfills a role similar to Function<List<Card>, Optional<Card>>.
However, defining a new, more specific interface makes its intent clearer in the code.
The custom interface provides several benefits:
first, lowestBlackCard, and highestFaceCard.
Unlike sets, lists typically allow duplicate elements. More formally,
lists typically allow pairs of elements e1 and e2
such that e1.equals(e2), and they typically allow multiple
null elements if they allow null elements at all. It is not inconceivable
that someone might wish to implement a list that prohibits duplicates, by
throwing runtime exceptions when the user attempts to insert them, but we
expect this usage to be rare.
The List interface places additional stipulations, beyond those
specified in the Collection interface, on the contracts of the
iterator, add, remove, equals, and
hashCode methods. Declarations for other inherited methods are
also included here for convenience.
The List interface provides four methods for positional (indexed)
access to list elements. Lists (like Java arrays) are zero based. Note
that these operations may execute in time proportional to the index value
for some implementations (the LinkedList class, for
example). Thus, iterating over the elements in a list is typically
preferable to indexing through it if the caller does not know the
implementation.
The List interface provides a special iterator, called a
ListIterator, that allows element insertion and replacement, and
bidirectional access in addition to the normal operations that the
Iterator interface provides. A method is provided to obtain a
list iterator that starts at a specified position in the list.
The List interface provides two methods to search for a specified
object. From a performance standpoint, these methods should be used with
caution. In many implementations they will perform costly linear
searches.
The List interface provides two methods to efficiently insert and
remove multiple elements at an arbitrary point in the list.
Note: While it is permissible for lists to contain themselves as elements,
extreme caution is advised: the equals and hashCode
methods are no longer well defined on such a list.
Some list implementations have restrictions on the elements that
they may contain. For example, some implementations prohibit null elements,
and some have restrictions on the types of their elements. Attempting to
add an ineligible element throws an unchecked exception, typically
NullPointerException or ClassCastException. Attempting
to query the presence of an ineligible element may throw an exception,
or it may simply return false; some implementations will exhibit the former
behavior and some will exhibit the latter. More generally, attempting an
operation on an ineligible element whose completion would not result in
the insertion of an ineligible element into the list may throw an
exception or it may succeed, at the option of the implementation.
Such exceptions are marked as "optional" in the specification for this
interface.
The List.of and
List.copyOf static factory methods
provide a convenient way to create unmodifiable lists. The List
instances created by these methods have the following characteristics:
UnsupportedOperationException to be thrown.
However, if the contained elements are themselves mutable,
this may cause the List's contents to appear to change.
null elements. Attempts to create them with
null elements result in NullPointerException.
subList views implement the
RandomAccess interface.
This interface is a member of the Java Collections Framework.
Optional describing the given non-null
value.Optional describing the given non-null
value.T - the type of the valuevalue - the value to describe, which must be non-nullOptional with the value presentNullPointerException - if value is nullindex - index of the element to returnIndexOutOfBoundsException - if the index is out of range
(index < 0 || index >= size())null value.
If a value is present, isPresent() returns true. If no
value is present, the object is considered empty and
isPresent() returns false.
null value.
If a value is present, isPresent() returns true. If no
value is present, the object is considered empty and
isPresent() returns false.
Additional methods that depend on the presence or absence of a contained
value are provided, such as orElse()
(returns a default value if no value is present) and
ifPresent() (performs an
action if a value is present).
This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail.
Optional is primarily intended for use as a method return type where
there is a clear need to represent "no result," and where using null
is likely to cause errors. A variable whose type is Optional should
never itself be null; it should always point to an Optional
instance.