/**
* Copyright (C) 2022 by Martin Robillard. See https://codesample.info/about.html
*/
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.
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.
index - index of the element to return
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())
Optional describing the given non-null value.
Optional describing the given non-null value.
T - the type of the value
value - the value to describe, which must be non-null
Optional with the value present
NullPointerException - if value is null