/*******************************************************************************
* 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.chapter4;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* Represents a deck of playing cards. In this version the class
* also defines a nested class Shuffler that can be used
* to shuffle a deck a remember the number of times it was
* shuffled.
*/
public class Deck implements CardSource {
private List<Card> aCards = new ArrayList<>();
/**
* Creates a new deck of 52 cards, shuffled.
*/
public Deck() {
shuffle();
}
/**
* Reinitializes the deck with all 52 cards, and shuffles them.
*/
public void shuffle() {
aCards.();
for( Suit suit : Suit.values() ) {
for( Rank rank : Rank.values() ) {
aCards.add( Card.get( rank, suit ));
}
}
Collections.shuffle(aCards);
}
/**
* Places pCard on top of the deck.
* @param pCard The card to place on top
* of the deck.
* @pre pCard !=null
*/
public void push(Card pCard) {
assert pCard != null;
aCards.add(pCard);
}
/**
* Draws a card from the deck: removes the card from the top
* of the deck and returns it.
* @return The card drawn.
* @pre !isEmpty()
*/
@Override
public Card draw() {
assert !isEmpty();
return aCards.remove(aCards.size() - 1);
}
/**
* @return True if and only if there are no cards in the deck.
*/
@Override
public boolean isEmpty() {
return aCards.isEmpty();
}
/**
* @return An instance of shuffler with this Deck as its outer instance.
*/
public Shuffler newShuffler() {
return ;
}
/**
* A class that can shuffle a deck and remember
* the number of shuffles.
*/
public class {
private Shuffler() {}
private int aNumberOfShuffles = 0;
public void shuffle() {
aNumberOfShuffles++;
.shuffle();
}
public int getNumberOfShuffles() {
return aNumberOfShuffles;
}
}
/**
* @param pRank The rank to use to compare the decks.
* @return A comparator that compares two decks based on the number of cards
* of rank pRank that they contains.
*
* Note that this version is improved from the code in the book,
* by avoiding the unnecessary parameter pRank in CountCards.
*/
public static Comparator<Deck> (Rank pRank) {
return new Comparator<Deck>() {
@Override
public int compare(Deck pDeck1, Deck pDeck2) {
return countCards(pDeck1) - countCards(pDeck2);
}
private int (Deck pDeck) {
int result = 0;
for( Card card : pDeck. ) {
if( card.getRank() == ) {
result++;
}
}
return result;
}
};
}
}To make sure there are no cards in the deck, we have to clear the existing
ArrayList, because field aCards is declared final, when prevents reinitializing
it with an new, empty, list.
To make sure there are no cards in the deck, we have to clear the existing
ArrayList, because field aCards is declared final, when prevents reinitializing
it with an new, empty, list.
Collections.sort or Arrays.sort) to allow precise control over the sort order.
Comparators can also be used to control the order of certain data
structures (such as sorted sets or
sorted maps), or to provide an ordering for
collections of objects that don't have a natural ordering.Collections.sort or Arrays.sort) to allow precise control over the sort order.
Comparators can also be used to control the order of certain data
structures (such as sorted sets or
sorted maps), or to provide an ordering for
collections of objects that don't have a natural ordering.
The ordering imposed by a comparator c on a set of elements
S is said to be consistent with equals if and only if
c.compare(e1, e2)==0 has the same boolean value as
e1.equals(e2) for every e1 and e2 in
S.
Caution should be exercised when using a comparator capable of imposing an
ordering inconsistent with equals to order a sorted set (or sorted map).
Suppose a sorted set (or sorted map) with an explicit comparator c
is used with elements (or keys) drawn from a set S. If the
ordering imposed by c on S is inconsistent with equals,
the sorted set (or sorted map) will behave "strangely." In particular the
sorted set (or sorted map) will violate the general contract for set (or
map), which is defined in terms of equals.
For example, suppose one adds two elements a and b such that
(a.equals(b) && c.compare(a, b) != 0)
to an empty TreeSet with comparator c.
The second add operation will return
true (and the size of the tree set will increase) because a and
b are not equivalent from the tree set's perspective, even though
this is contrary to the specification of the
Set.add method.
Note: It is generally a good idea for comparators to also implement
java.io.Serializable, as they may be used as ordering methods in
serializable data structures (like TreeSet, TreeMap). In
order for the data structure to serialize successfully, the comparator (if
provided) must implement Serializable.
For the mathematically inclined, the relation that defines the
imposed ordering that a given comparator c imposes on a
given set of objects S is:
{(x, y) such that c.compare(x, y) <= 0}.
The quotient for this total order is: {(x, y) such that c.compare(x, y) == 0}.
It follows immediately from the contract for compare that the
quotient is an equivalence relation on S, and that the
imposed ordering is a total order on S. When we say that
the ordering imposed by c on S is consistent with
equals, we mean that the quotient for the ordering is the equivalence
relation defined by the objects' equals(Object) method(s): {(x, y) such that x.equals(y)}.
In other words, when the imposed ordering is consistent with
equals, the equivalence classes defined by the equivalence relation
of the equals method and the equivalence classes defined by
the quotient of the compare method are the same.
Unlike Comparable, a comparator may optionally permit
comparison of null arguments, while maintaining the requirements for
an equivalence relation.
This interface is a member of the Java Collections Framework.
The methods of this class all throw a NullPointerException
if the collections or class objects provided to them are null.
The documentation for the polymorphic algorithms contained in this class
generally includes a brief description of the implementation. Such
descriptions should be regarded as implementation notes, rather than
parts of the specification. Implementors should feel free to
substitute other algorithms, so long as the specification itself is adhered
to. (For example, the algorithm used by sort does not have to be
a mergesort, but it does have to be stable.)
The "destructive" algorithms contained in this class, that is, the
algorithms that modify the collection on which they operate, are specified
to throw UnsupportedOperationException if the collection does not
support the appropriate mutation primitive(s), such as the set
method. These algorithms may, but are not required to, throw this
exception if an invocation would have no effect on the collection. For
example, invoking the sort method on an unmodifiable list that is
already sorted may or may not throw UnsupportedOperationException.
This class is a member of the Java Collections Framework.
The instance, however, can be mutated: as it's the case with this class,
the content of the list aCards changes. So the final keyword doesn't
indicate that the field is immutable, or that a class with only final
fields is immutable itself.
The instance, however, can be mutated: as it's the case with this class,
the content of the list aCards changes. So the final keyword doesn't
indicate that the field is immutable, or that a class with only final
fields is immutable itself.
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.
This is a static factory method because it creates a new object of
type Comparator that is not related to any instance of class Deck.
This is a static factory method because it creates a new object of
type Comparator that is not related to any instance of class Deck.
Creates and instantiates a subtype of Comparator<Deck>.
Creates and instantiates a subtype of Comparator<Deck>.
Literal reference to the outer instance of this instance of Shuffle.
Literal reference to the outer instance of this instance of Shuffle.
As mentioned in Chapter 3's annotation, an alternative to clearing the list is to
create a new one (aCards = new ArrayList<>();). Of course, the field would no longer
be final. In that alternative implementation, it would be necessary to ensure that no
method keeps an old reference to aCards after it may have been reassigned.
As mentioned in Chapter 3's annotation, an alternative to clearing the list is to
create a new one (aCards = new ArrayList<>();). Of course, the field would no longer
be final. In that alternative implementation, it would be necessary to ensure that no
method keeps an old reference to aCards after it may have been reassigned.
This statement will create an new instance of Shuffler with an implicit field
that refers to an outer instance. In this case, the outer instance is the instance
of class Deck that received the method call to newShuffler().
This statement will create an new instance of Shuffler with an implicit field
that refers to an outer instance. In this case, the outer instance is the instance
of class Deck that received the method call to newShuffler().
This may seem counter-intuitive. Fields (and methods) that are private are visible when inside the class that declares those fields, even if it's within the context of another class, like the anonymous class declaration here.
This may seem counter-intuitive. Fields (and methods) that are private are visible when inside the class that declares those fields, even if it's within the context of another class, like the anonymous class declaration here.
Notice how pRank refers to the parameter of the method
in which this class is declared. As a result, instances of the anonymous Comparator class
will receive an implicit field that refers to whatever object pRank was referring to when
the method was called. This is called capturing a variable, and the resulting instance of the anonymous
class becomes a special program element similar to what is called a closure in functional
programming languages.
Notice how pRank refers to the parameter of the method
in which this class is declared. As a result, instances of the anonymous Comparator class
will receive an implicit field that refers to whatever object pRank was referring to when
the method was called. This is called capturing a variable, and the resulting instance of the anonymous
class becomes a special program element similar to what is called a closure in functional
programming languages.
Anonymous classes can declare fields and methods just like
any other classes. The role of this method is to simplify the code
of method compare.
Anonymous classes can declare fields and methods just like
any other classes. The role of this method is to simplify the code
of method compare.
One of the reasons for locating the static factory method createByRankComparator inside
of class Deck is that it allows us to refer to the
of Deck, which would not have been possible otherwise.
One of the reasons for locating the static factory method createByRankComparator inside
of class Deck is that it allows us to refer to the
of Deck, which would not have been possible otherwise.
Notice that this class is declared inside class Deck. Because it not declared
static, instance of Shuffler will have an implicit reference to an outer instance of
of their parent type (Deck).
Chapter 4, insight #8
Remember that additional data can be attached to instances of inner classes, either in the form of a reference to an instance of an outer class, or as copies of local variables bundled in a closure.
Notice that this class is declared inside class Deck. Because it not declared
static, instance of Shuffler will have an implicit reference to an outer instance of
of their parent type (Deck).
Chapter 4, insight #8
Remember that additional data can be attached to instances of inner classes, either in the form of a reference to an instance of an outer class, or as copies of local variables bundled in a closure.
Use of the keyword final here means that aCards will only
ever refer to that one of ArrayList that is created here.
Chapter 4, insight #4
Consider declaring instance variables final whenever possible
Use of the keyword final here means that aCards will only
ever refer to that one of ArrayList that is created here.
Chapter 4, insight #4
Consider declaring instance variables final whenever possible
List interface. Implements
all optional list operations, and permits all elements, including
null. In addition to implementing the List interface,
this class provides methods to manipulate the size of the array that is
used internally to store the list. (This class is roughly equivalent to
Vector, except that it is unsynchronized.)
List interface. Implements
all optional list operations, and permits all elements, including
null. In addition to implementing the List interface,
this class provides methods to manipulate the size of the array that is
used internally to store the list. (This class is roughly equivalent to
Vector, except that it is unsynchronized.)
The size, isEmpty, get, set,
iterator, and listIterator operations run in constant
time. The add operation runs in amortized constant time,
that is, adding n elements requires O(n) time. All of the other operations
run in linear time (roughly speaking). The constant factor is low compared
to that for the LinkedList implementation.
Each ArrayList instance has a capacity. The capacity is
the size of the array used to store the elements in the list. It is always
at least as large as the list size. As elements are added to an ArrayList,
its capacity grows automatically. The details of the growth policy are not
specified beyond the fact that adding an element has constant amortized
time cost.
An application can increase the capacity of an ArrayList instance
before adding a large number of elements using the ensureCapacity
operation. This may reduce the amount of incremental reallocation.
Note that this implementation is not synchronized.
If multiple threads access an ArrayList instance concurrently,
and at least one of the threads modifies the list structurally, it
must be synchronized externally. (A structural modification is
any operation that adds or deletes one or more elements, or explicitly
resizes the backing array; merely setting the value of an element is not
a structural modification.) This is typically accomplished by
synchronizing on some object that naturally encapsulates the list.
If no such object exists, the list should be "wrapped" using the
Collections.synchronizedList
method. This is best done at creation time, to prevent accidental
unsynchronized access to the list:
List list = Collections.synchronizedList(new ArrayList(...));
The iterators returned by this class's iterator and
listIterator methods are fail-fast:
if the list is structurally modified at any time after the iterator is
created, in any way except through the iterator's own
remove or
add methods, the iterator will throw a
ConcurrentModificationException. Thus, in the face of
concurrent modification, the iterator fails quickly and cleanly, rather
than risking arbitrary, non-deterministic behavior at an undetermined
time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class is a member of the Java Collections Framework.