AbstractSet (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.util.AbstractCollection
  • • java.util.AbstractSet

• Type Parameters:
  E - the type of elements maintained by this set
  All Implemented Interfaces:
  Iterable, Collection, Set
  Direct Known Subclasses:
  ConcurrentSkipListSet, CopyOnWriteArraySet, EnumSet, HashSet, TreeSet

public abstract class AbstractSet
extends AbstractCollection
implements Set
This class provides a skeletal implementation of the
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:
Collection, AbstractCollection, Set

• • Constructor Summary

  Constructors

  Modifier	Constructor	Description
  protected	AbstractSet()	Sole constructor.

  • Method Summary

  All Methods Instance Methods Concrete Methods

  Modifier and Type	Method	Description
  boolean	equals(Object o)	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](../../java/util/AbstractCollection.html "class in java.util")  
     `[add](../../java/util/AbstractCollection.html#add-E-), [addAll](../../java/util/AbstractCollection.html#addAll-java.util.Collection-), [clear](../../java/util/AbstractCollection.html#clear--), [contains](../../java/util/AbstractCollection.html#contains-java.lang.Object-), [containsAll](../../java/util/AbstractCollection.html#containsAll-java.util.Collection-), [isEmpty](../../java/util/AbstractCollection.html#isEmpty--), [iterator](../../java/util/AbstractCollection.html#iterator--), [remove](../../java/util/AbstractCollection.html#remove-java.lang.Object-), [retainAll](../../java/util/AbstractCollection.html#retainAll-java.util.Collection-), [size](../../java/util/AbstractCollection.html#size--), [toArray](../../java/util/AbstractCollection.html#toArray--), [toArray](../../java/util/AbstractCollection.html#toArray-T:A-), [toString](../../java/util/AbstractCollection.html#toString--)`  
     * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
     `[clone](../../java/lang/Object.html#clone--), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`  
     * ### Methods inherited from interface java.util.[Set](../../java/util/Set.html "interface in java.util")  
     `[add](../../java/util/Set.html#add-E-), [addAll](../../java/util/Set.html#addAll-java.util.Collection-), [clear](../../java/util/Set.html#clear--), [contains](../../java/util/Set.html#contains-java.lang.Object-), [containsAll](../../java/util/Set.html#containsAll-java.util.Collection-), [isEmpty](../../java/util/Set.html#isEmpty--), [iterator](../../java/util/Set.html#iterator--), [remove](../../java/util/Set.html#remove-java.lang.Object-), [retainAll](../../java/util/Set.html#retainAll-java.util.Collection-), [size](../../java/util/Set.html#size--), [spliterator](../../java/util/Set.html#spliterator--), [toArray](../../java/util/Set.html#toArray--), [toArray](../../java/util/Set.html#toArray-T:A-)`  
     * ### Methods inherited from interface java.util.[Collection](../../java/util/Collection.html "interface in java.util")  
     `[parallelStream](../../java/util/Collection.html#parallelStream--), [removeIf](../../java/util/Collection.html#removeIf-java.util.function.Predicate-), [stream](../../java/util/Collection.html#stream--)`  
     * ### Methods inherited from interface java.lang.[Iterable](../../java/lang/Iterable.html "interface in java.lang")  
     `[forEach](../../java/lang/Iterable.html#forEach-java.util.function.Consumer-)`

• • Constructor Detail

     * #### AbstractSet  
     protected AbstractSet()  
     Sole constructor. (For invocation by subclass constructors, typically implicit.)  

  • Method Detail

    * #### equals  
    public boolean equals([Object](../../java/lang/Object.html "class in java.lang") o)  
    Compares the specified object with this set for equality. Returns  
    true  
     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 the  
    equals  
     method works properly across different implementations of the  
    Set  
     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).  
    Specified by:  
    `[equals](../../java/util/Collection.html#equals-java.lang.Object-)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Specified by:  
    `[equals](../../java/util/Set.html#equals-java.lang.Object-)` in interface `[Set](../../java/util/Set.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Overrides:  
    `[equals](../../java/lang/Object.html#equals-java.lang.Object-)` in class `[Object](../../java/lang/Object.html "class in java.lang")`  
    Parameters:  
    `o` \- object to be compared for equality with this set  
    Returns:  
    true if the specified object is equal to this set  
    See Also:  
    [Object.hashCode()](../../java/lang/Object.html#hashCode--), [HashMap](../../java/util/HashMap.html "class in java.util")  
    * #### 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 a  
    null  
     element is defined to be zero. This ensures that  
    s1.equals(s2)  
     implies that  
    s1.hashCode()==s2.hashCode()  
     for any two sets  
    s1  
     and  
    s2  
    , as required by the general contract of[Object.hashCode()](../../java/lang/Object.html#hashCode--).  
    This implementation iterates over the set, calling thehashCode method on each element in the set, and adding up the results.  
    Specified by:  
    `[hashCode](../../java/util/Collection.html#hashCode--)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Specified by:  
    `[hashCode](../../java/util/Set.html#hashCode--)` in interface `[Set](../../java/util/Set.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Overrides:  
    `[hashCode](../../java/lang/Object.html#hashCode--)` in class `[Object](../../java/lang/Object.html "class in java.lang")`  
    Returns:  
    the hash code value for this set  
    See Also:  
    [Object.equals(Object)](../../java/lang/Object.html#equals-java.lang.Object-), [Set.equals(Object)](../../java/util/Set.html#equals-java.lang.Object-)  
    * #### removeAll  
    public boolean removeAll([Collection](../../java/util/Collection.html "interface in java.util")<?> 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 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's remove 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's remove method.  
    Note that this implementation will throw anUnsupportedOperationException if the iterator returned by theiterator method does not implement the remove method.  
    Specified by:  
    `[removeAll](../../java/util/Collection.html#removeAll-java.util.Collection-)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Specified by:  
    `[removeAll](../../java/util/Set.html#removeAll-java.util.Collection-)` in interface `[Set](../../java/util/Set.html "interface in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    Overrides:  
    `[removeAll](../../java/util/AbstractCollection.html#removeAll-java.util.Collection-)` in class `[AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractSet.html "type parameter in AbstractSet")>`  
    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](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the removeAll operation is not supported by this set  
    `[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the class of an element of this set is incompatible with the specified collection ([optional](Collection.html#optional-restrictions))  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if this set contains a null element and the specified collection does not permit null elements ([optional](Collection.html#optional-restrictions)), or if the specified collection is null  
    See Also:  
    [AbstractCollection.remove(Object)](../../java/util/AbstractCollection.html#remove-java.lang.Object-), [AbstractCollection.contains(Object)](../../java/util/AbstractCollection.html#contains-java.lang.Object-)

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