- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.AbstractSet<E>
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- 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
public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E>
This class provides a skeletal implementation of theSetinterface 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
Setinterface (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
AbstractCollectionclass. It merely adds implementations forequalsandhashCode.This class is a member of the Java Collections Framework.
- Since:
- 1.2
- See Also:
Collection,AbstractCollection,Set
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Constructor Summary
Constructors Modifier Constructor Description protectedAbstractSet()Sole constructor.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description booleanequals(Object o)Compares the specified object with this set for equality.inthashCode()Returns the hash code value for this set.booleanremoveAll(Collection<?> c)Removes from this set all of its elements that are contained in the specified collection (optional operation).-
Methods declared in class java.util.AbstractCollection
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, toArray, toArray, toString
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Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.Collection
parallelStream, removeIf, stream, toArray
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Method Detail
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equals
public boolean equals(Object o)
Compares the specified object with this set for equality. Returnstrueif 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 theequalsmethod works properly across different implementations of theSetinterface.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).- Specified by:
equalsin interfaceCollection<E>- Specified by:
equalsin interfaceSet<E>- Overrides:
equalsin classObject- Parameters:
o- object to be compared for equality with this set- Returns:
trueif the specified object is equal to this set- See Also:
Object.hashCode(),HashMap
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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 anullelement is defined to be zero. This ensures thats1.equals(s2)implies thats1.hashCode()==s2.hashCode()for any two setss1ands2, as required by the general contract ofObject.hashCode().This implementation iterates over the set, calling the
hashCodemethod on each element in the set, and adding up the results.- Specified by:
hashCodein interfaceCollection<E>- Specified by:
hashCodein interfaceSet<E>- Overrides:
hashCodein classObject- Returns:
- the hash code value for this set
- See Also:
Object.equals(Object),Set.equals(Object)
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removeAll
public boolean removeAll(Collection<?> c)
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
sizemethod 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'sremovemethod. 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'sremovemethod.Note that this implementation will throw an
UnsupportedOperationExceptionif the iterator returned by theiteratormethod does not implement theremovemethod.- Specified by:
removeAllin interfaceCollection<E>- Specified by:
removeAllin interfaceSet<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be removed from this set- Returns:
trueif this set changed as a result of the call- Throws:
UnsupportedOperationException- if theremoveAlloperation 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:
AbstractCollection.remove(Object),AbstractCollection.contains(Object)
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