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Class com.sun.java.util.collections.HashSet
java.lang.Object
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+----com.sun.java.util.collections.AbstractCollection
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+----com.sun.java.util.collections.AbstractSet
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+----com.sun.java.util.collections.HashSet
- public class HashSet
- extends AbstractSet
- implements Set, Cloneable, Serializable
This class implements the Set interface, backed by a hash table
(actually a HashMap instance). It makes no guarantees as to the
iteration order of the set; in particular, it does not guarantee that the
order will remain constant over time. This class permits the null
element.
This class offers constant time performance for the basic operations
(add, remove, contains and size),
assuming the hash function disperses the elements properly among the
buckets. Iterating over this set requires time proportional to the sum of
the HashSet instance's size (the number of elements) plus the
"capacity" of the backing HashMap instance (the number of
buckets). Thus, it's very important not to set the intial capacity too
high (or the load factor too low) if iteration performance is important.
Note that this implementation is not synchronized. If multiple
threads access a set concurrently, and at least one of the threads modifies
the set, it must be synchronized externally. This is typically
accomplished by synchronizing on some object that naturally encapsulates
the set. If no such object exists, the set should be "wrapped" using the
Collections.synchronizedSet method. This is best done at creation
time, to prevent accidental unsynchronized access to the HashSet
instance:
Set s = Collections.synchronizedSet(new HashSet(...));
The iterators returned by this class's iterator method are
fail-fast: if the set is modified at any time after the iterator is
created, in any way except through the iterator's own remove
method, the Iterator throws 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.
- See Also:
- Collection, Set, TreeSet, synchronizedSet, HashMap
-
HashSet()
- Constructs a new, empty set; the backing HashMap instance has
default capacity and load factor, which is 0.75.
-
HashSet(Collection)
- Constructs a new set containing the elements in the specified
collection.
-
HashSet(int)
- Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and default load factor, which is
0.75.
-
HashSet(int, float)
- Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and the specified load factor.
-
add(Object)
- Adds the specified element to this set if it is not already
present.
-
clear()
- Removes all of the elements from this set.
-
clone()
- Returns a shallow copy of this HashSet instance: the elements
themselves are not cloned.
-
contains(Object)
- Returns true if this set contains the specified element.
-
isEmpty()
- Returns true if this set contains no elements.
-
iterator()
- Returns an iterator over the elements in this set.
-
remove(Object)
- Removes the given element from this set if it is present.
-
size()
- Returns the number of elements in this set (its cardinality).
HashSet
public HashSet()
- Constructs a new, empty set; the backing HashMap instance has
default capacity and load factor, which is 0.75.
HashSet
public HashSet(Collection c)
- Constructs a new set containing the elements in the specified
collection. The capacity of the backing HashMap instance is
twice the size of the specified collection or eleven (whichever is
greater), and the default load factor (which is 0.75) is used.
HashSet
public HashSet(int initialCapacity,
float loadFactor)
- Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and the specified load factor.
- Parameters:
- initialCapacity - the initial capacity of the hash map.
- loadFactor - the load factor of the hash map.
HashSet
public HashSet(int initialCapacity)
- Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and default load factor, which is
0.75.
- Parameters:
- initialCapacity - the initial capacity of the hash table.
iterator
public Iterator iterator()
- Returns an iterator over the elements in this set. The elements
are returned in no particular order.
- Returns:
- an Iterator over the elements in this set.
- Overrides:
- iterator in class AbstractCollection
- See Also:
- ConcurrentModificationException
size
public int size()
- Returns the number of elements in this set (its cardinality).
- Returns:
- the number of elements in this set (its cardinality).
- Overrides:
- size in class AbstractCollection
isEmpty
public boolean isEmpty()
- Returns true if this set contains no elements.
- Returns:
- true if this set contains no elements.
- Overrides:
- isEmpty in class AbstractCollection
contains
public boolean contains(Object o)
- Returns true if this set contains the specified element.
- Returns:
- true if this set contains the specified element.
- Overrides:
- contains in class AbstractCollection
add
public boolean add(Object o)
- Adds the specified element to this set if it is not already
present.
- Parameters:
- o - element to be added to this set.
- Returns:
- true if the set did not already contain the specified
element.
- Overrides:
- add in class AbstractCollection
remove
public boolean remove(Object o)
- Removes the given element from this set if it is present.
- Parameters:
- o - object to be removed from this set, if present.
- Returns:
- true if the set contained the specified element.
- Overrides:
- remove in class AbstractCollection
clear
public void clear()
- Removes all of the elements from this set.
- Overrides:
- clear in class AbstractCollection
clone
public Object clone()
- Returns a shallow copy of this HashSet instance: the elements
themselves are not cloned.
- Returns:
- a shallow copy of this set.
- Overrides:
- clone in class Object
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