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FlexDoc/Javadoc 2.0 Demo Java Doc |
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 initial 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 hash 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 set:
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.
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.
Constructor Summary |
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HashSet()
Constructs a new, empty set; the backing HashMap instance has
default initial capacity (16) and load factor (0.75).
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Constructs a new set containing the elements in the specified
collection.
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HashSet(int initialCapacity)
Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and default load factor (0.75).
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HashSet(int initialCapacity, float loadFactor)
Constructs a new, empty set; the backing HashMap instance has
the specified initial capacity and the specified load factor.
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Method Summary |
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boolean |
Adds the specified element to this set if it is not already present.
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void |
clear()
Removes all of the elements from this set.
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clone()
Returns a shallow copy of this HashSet instance: the elements
themselves are not cloned.
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boolean |
Returns true if this set contains the specified element.
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boolean |
isEmpty()
Returns true if this set contains no elements.
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iterator()
Returns an iterator over the elements in this set.
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boolean |
Removes the specified element from this set if it is present.
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int |
size()
Returns the number of elements in this set (its cardinality).
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Creates a late-binding
and fail-fast Spliterator over the elements in this
set.
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Object[] |
toArray()
Returns an array containing all of the elements in this collection.
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Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
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Methods inherited from class java.util.AbstractSet |
Methods inherited from class java.util.AbstractCollection |
Methods inherited from class java.lang.Object |
Methods inherited from interface java.util.Collection |
Methods inherited from interface java.lang.Iterable |
Methods inherited from interface java.util.Set |
public HashSet |
() |
public HashSet |
(Collection<? extends E> c) |
public HashSet |
(int initialCapacity, float loadFactor) |
public HashSet |
(int initialCapacity) |
() |
public int size |
() |
public boolean isEmpty |
() |
public boolean contains |
(Object o) |
public boolean add |
(E e) |
public boolean remove |
(Object o) |
public void clear |
() |
public Object clone |
() |
() |
The Spliterator reports Spliterator.SIZED and Spliterator.DISTINCT. Overriding implementations should document the reporting of additional characteristic values.
public Object[] toArray |
() |
The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
(T[] a) |
If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
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FlexDoc/Javadoc 2.0 Demo Java Doc |