java.util.HashSet Maven / Gradle / Ivy
/*
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stub files, must be accompanied by this notice in its entirety.
This work corresponds to the API signatures of JSR 219: Foundation
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*/
package java.util;
/**
* 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 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 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.
*
*
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.
*
* @author Josh Bloch
* @version 1.19, 02/02/00
* @see Collection
* @see Set
* @see TreeSet
* @see Collections#synchronizedSet(Set)
* @see HashMap
* @since 1.2
*/
public class HashSet extends AbstractSet
implements Set, Cloneable, java.io.Serializable
{
static final long serialVersionUID = -5024744406713321676L;
/**
* Constructs a new, empty set; the backing HashMap instance has
* default initial capacity (16) and load factor (0.75).
*/
public HashSet() { }
/**
* Constructs a new set containing the elements in the specified
* collection. The HashMap is created with default load factor
* (0.75) and an initial capacity sufficient to contain the elements in
* the specified collection.
*
* @param c the collection whose elements are to be placed into this set.
* @throws NullPointerException if the specified collection is null.
*/
public HashSet(Collection c) { }
/**
* Constructs a new, empty set; the backing HashMap instance has
* the specified initial capacity and the specified load factor.
*
* @param initialCapacity the initial capacity of the hash map.
* @param loadFactor the load factor of the hash map.
* @throws IllegalArgumentException if the initial capacity is less
* than zero, or if the load factor is nonpositive.
*/
public HashSet(int initialCapacity, float loadFactor) { }
/**
* Constructs a new, empty set; the backing HashMap instance has
* the specified initial capacity and default load factor, which is
* 0.75.
*
* @param initialCapacity the initial capacity of the hash table.
* @throws IllegalArgumentException if the initial capacity is less
* than zero.
*/
public HashSet(int initialCapacity) { }
/**
* Returns an iterator over the elements in this set. The elements
* are returned in no particular order.
*
* @return an Iterator over the elements in this set.
* @see ConcurrentModificationException
*/
public Iterator iterator() {
return null;
}
/**
* Returns the number of elements in this set (its cardinality).
*
* @return the number of elements in this set (its cardinality).
*/
public int size() {
return 0;
}
/**
* Returns true if this set contains no elements.
*
* @return true if this set contains no elements.
*/
public boolean isEmpty() {
return false;
}
/**
* Returns true if this set contains the specified element.
*
* @param o element whose presence in this set is to be tested.
* @return true if this set contains the specified element.
*/
public boolean contains(Object o) {
return false;
}
/**
* Adds the specified element to this set if it is not already
* present.
*
* @param o element to be added to this set.
* @return true if the set did not already contain the specified
* element.
*/
public boolean add(Object o) {
return false;
}
/**
* Removes the specified element from this set if it is present.
*
* @param o object to be removed from this set, if present.
* @return true if the set contained the specified element.
*/
public boolean remove(Object o) {
return false;
}
/**
* Removes all of the elements from this set.
*/
public void clear() { }
/**
* Returns a shallow copy of this HashSet instance: the elements
* themselves are not cloned.
*
* @return a shallow copy of this set.
*/
public Object clone() {
return null;
}
/**
* Reconstitute the HashSet instance from a stream (that is,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException
{ }
/**
* Save the state of this HashSet instance to a stream (that is,
* serialize this set).
*
* @serialData The capacity of the backing HashMap instance
* (int), and its load factor (float) are emitted, followed by
* the size of the set (the number of elements it contains)
* (int), followed by all of its elements (each an Object) in
* no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException
{ }
}