/*******************************************************************************
* 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.chapter3;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
/**
* Represents a deck of playing cards. In this version, the cards in the
* deck are stored in a list and the list of cards in the deck can
* be obtained by client code using an immutable wrapper object.
*
* This version of the Deck class also implements {@link CardSource}
* and has a sort() method to demonstrate the use of comparators.
*
* The Deck is also iterable: it fulfills the role of ConcreteIterable
* in the Iterator design pattern.
*/
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.clear();
for( Suit suit : Suit.values() ) {
for( Rank rank : Rank.values() ) {
aCards.add( new Card( 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 unmodifiable list of all the cards in the deck.
*/
public List<Card> {
return Collections.unmodifiableList(aCards);
}
/**
* Sorts the cards in the deck by ascending rank.
*/
public void sort() {
Collections.sort(aCards, new () {
@Override
public int compare(Card pCard1, Card pCard2) {
return pCard1.getRank().compareTo(pCard2.getRank());
}
});
}
@Override
public Iterator<Card> {
return aCards.iterator();
}
}
An alternative to clearing the list would be to create a new one. However, clearing the list makes the program easier to understand, because we only have one list object to track. This notion is covered in detail in Chapter 4.
An alternative to clearing the list would be to create a new one. However, clearing the list makes the program easier to understand, because we only have one list object to track. This notion is covered in detail in Chapter 4.
Iterator takes the place of
Enumeration in the Java Collections Framework. Iterators
differ from enumerations in two ways:
Iterator takes the place of
Enumeration in the Java Collections Framework. Iterators
differ from enumerations in two ways:
This interface is a member of the Java Collections Framework.
Enumeration can be converted into an Iterator by
using the Enumeration.asIterator() method.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.
This statement illustrates the concept of delegation, which we will revisit in
Chapter 6. The contract of the interface requires this method to return an object
of type Iterator. Instead of creating an new Iterator, this method requests
the iterator object provided by the underlying list stored in field aCards, and returns it
instead. The iterator supplied by ArrayList works here because it's an iterator
over Card objects that will provide an iteration over exactly the sequence of cards
represented by the Deck. Note that this code technically breaks encapsulation because
interface Iterator has a remove method that changes the underlying collection. However,
for simplicity, we assume that by convention, this remove method will never be called in our code.
This statement illustrates the concept of delegation, which we will revisit in
Chapter 6. The contract of the interface requires this method to return an object
of type Iterator. Instead of creating an new Iterator, this method requests
the iterator object provided by the underlying list stored in field aCards, and returns it
instead. The iterator supplied by ArrayList works here because it's an iterator
over Card objects that will provide an iteration over exactly the sequence of cards
represented by the Deck. Note that this code technically breaks encapsulation because
interface Iterator has a remove method that changes the underlying collection. However,
for simplicity, we assume that by convention, this remove method will never be called in our code.
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 code supplies an anonymous function object of type Comparator<Card>
as second argument to method sort.
This code supplies an anonymous function object of type Comparator<Card>
as second argument to method sort.
This method returns an object that fulfills the role of the iterator in the Iterator design pattern. The return type of the method is an abstract iterator (an interface), but the method returns a concrete iterator (an actual object).
This method returns an object that fulfills the role of the iterator in the Iterator design pattern. The return type of the method is an abstract iterator (an interface), but the method returns a concrete iterator (an actual object).
This method illustrates a way to obtain all the cards in the deck without breaking encapsulation. It relies on a library method that returns an unmodifiable view of the field.
This method illustrates a way to obtain all the cards in the deck without breaking encapsulation. It relies on a library method that returns an unmodifiable view of the field.
This code takes advantage of the static method values(), which
is implicitly defined on any enumerated type. This method returns
an array of all the enumerated values for the type, in their declaration order.
This code takes advantage of the static method values(), which
is implicitly defined on any enumerated type. This method returns
an array of all the enumerated values for the type, in their declaration order.
The main difference between Comparable and Comparator is that Comparable
is implemented by the objects that are being compared, whereas Comparator
is implemented by some other object that does the comparison. For this
reason, method compare of Comparator requires to pass in both
objects being compared.
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 main difference between Comparable and Comparator is that Comparable
is implemented by the objects that are being compared, whereas Comparator
is implemented by some other object that does the comparison. For this
reason, method compare of Comparator requires to pass in both
objects being compared.
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.
Defines the role of the abstract iterable in the Iterator design pattern. An abstract iterable is any object on which it is possible to iterate.
Chapter 3, insight #4
Use library interface types, such as Comparable, to implement commonly expected behavior
for statement (sometimes called the "for-each loop" statement).Defines the role of the abstract iterable in the Iterator design pattern. An abstract iterable is any object on which it is possible to iterate.
Chapter 3, insight #4
Use library interface types, such as Comparable, to implement commonly expected behavior
for statement (sometimes called the "for-each loop" statement).for statementList 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.