/**
* Copyright (C) 2022 by Martin Robillard. See https://codesample.info/about.html
*/
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;
}
};
}
}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.
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().
Literal reference to the outer instance of this instance of Shuffle.
Literal reference to the outer instance of this instance of Shuffle.
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>.
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.
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.
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.
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.
clear in interface Collection<E>
UnsupportedOperationException - if the clear operation is not supported by this list
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.
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.
Lists that support this operation may place limitations on what elements may be added to this list. In particular, some lists will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. List classes should clearly specify in their documentation any restrictions on what elements may be added.
add in interface Collection<E>
e - element to be appended to this list
true (as specified by Collection.add(E))
UnsupportedOperationException - if the add operation is not supported by this list
ClassCastException - if the class of the specified element prevents it from being added to this list
NullPointerException - if the specified element is null and this list does not permit null elements
IllegalArgumentException - if some property of this element prevents it from being added to this list
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 hedge "approximately" is used in the foregoing description because default source of randomness is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm would choose permutations with perfect uniformity.
This implementation traverses the list backwards, from the last element up to the second, repeatedly swapping a randomly selected element into the "current position". Elements are randomly selected from the portion of the list that runs from the first element to the current position, inclusive.
RandomAccess interface and is large, this implementation dumps the specified list into an array before shuffling it, and dumps the shuffled array back into the list. This avoids the quadratic behavior that would result from shuffling a "sequential access" list in place.
list - the list to be shuffled.
UnsupportedOperationException - if the specified list or its list-iterator does not support the set operation.
Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
size in interface Collection<E>
index - the index of the element to be removed
UnsupportedOperationException - if the remove operation is not supported by this list
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())
true if this list contains no elements.
true if this list contains no elements.
isEmpty in interface Collection<E>
true if this list contains no elements
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.