Class AbstractSet<E>
- Type Parameters:
E
- the type of elements maintained by this set
- All Implemented Interfaces:
Iterable<E>
,Collection<E>
,Set<E>
- Direct Known Subclasses:
ConcurrentSkipListSet
,CopyOnWriteArraySet
,EnumSet
,HashSet
,TreeSet
Set
interface to minimize the effort required to implement this
interface.
The process of implementing a set by extending this class is identical
to that of implementing a Collection by extending AbstractCollection,
except that all of the methods and constructors in subclasses of this
class must obey the additional constraints imposed by the Set
interface (for instance, the add method must not permit addition of
multiple instances of an object to a set).
Note that this class does not override any of the implementations from
the AbstractCollection
class. It merely adds implementations
for equals
and hashCode
.
This class is a member of the Java Collections Framework.
- Since:
- 1.2
- See Also:
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionboolean
Compares the specified object with this set for equality.int
hashCode()
Returns the hash code value for this set.boolean
removeAll
(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).Methods inherited from class java.util.AbstractCollection
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, size, toArray, toArray, toString
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Collection
parallelStream, removeIf, stream, toArray
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Constructor Details
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AbstractSet
protected AbstractSet()Sole constructor. (For invocation by subclass constructors, typically implicit.)
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Method Details
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equals
Compares the specified object with this set for equality. Returnstrue
if the given object is also a set, the two sets have the same size, and every member of the given set is contained in this set. This ensures that theequals
method works properly across different implementations of theSet
interface.This implementation first checks if the specified object is this set; if so it returns
true
. Then, it checks if the specified object is a set whose size is identical to the size of this set; if not, it returns false. If so, it returnscontainsAll((Collection) o)
. -
hashCode
public int hashCode()Returns the hash code value for this set. The hash code of a set is defined to be the sum of the hash codes of the elements in the set, where the hash code of anull
element is defined to be zero. This ensures thats1.equals(s2)
implies thats1.hashCode()==s2.hashCode()
for any two setss1
ands2
, as required by the general contract ofObject.hashCode()
.This implementation iterates over the set, calling the
hashCode
method on each element in the set, and adding up the results. -
removeAll
Removes from this set all of its elements that are contained in the specified collection (optional operation). If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.This implementation determines which is the smaller of this set and the specified collection, by invoking the
size
method on each. If this set has fewer elements, then the implementation iterates over this set, checking each element returned by the iterator in turn to see if it is contained in the specified collection. If it is so contained, it is removed from this set with the iterator'sremove
method. If the specified collection has fewer elements, then the implementation iterates over the specified collection, removing from this set each element returned by the iterator, using this set'sremove
method.Note that this implementation will throw an
UnsupportedOperationException
if the iterator returned by theiterator
method does not implement theremove
method.- Specified by:
removeAll
in interfaceCollection<E>
- Specified by:
removeAll
in interfaceSet<E>
- Overrides:
removeAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be removed from this set- Returns:
true
if this set changed as a result of the call- Throws:
UnsupportedOperationException
- if theremoveAll
operation is not supported by this setClassCastException
- if the class of an element of this set is incompatible with the specified collection (optional)NullPointerException
- if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
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