/*
 
* Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
 
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 
*
 
* This code is free software; you can redistribute it and/or modify it
 
* under the terms of the GNU General Public License version 2 only, as
 
* published by the Free Software Foundation.
  
Oracle designates this
 
* particular file as subject to the "Classpath" exception as provided
 
* by Oracle in the LICENSE file that accompanied this code.
 
*
 
* This code is distributed in the hope that it will be useful, but WITHOUT
 
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 
* FITNESS FOR A PARTICULAR PURPOSE.
  
See the GNU General Public License
 
* version 2 for more details (a copy is included in the LICENSE file that
 
* accompanied this code).
 
*
 
* You should have received a copy of the GNU General Public License version
 
* 2 along with this work; if not, write to the Free Software Foundation,
 
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 
*
 
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 
* or visit www.oracle.com if you need additional information or have any
 
* questions.
 
*/

package java.util;

import java.io.InvalidObjectException;
import sun.misc.SharedSecrets;

/**
 
* This class implements the <tt>Set</tt> interface, backed by a hash table
 
* (actually a <tt>HashMap</tt> 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 <tt>null</tt>
 
* element.
 
*
 
* <p>This class offers constant time performance for the basic operations
 
* (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>),
 
* assuming the hash function disperses the elements properly among the
 
* buckets.
  
Iterating over this set requires time proportional to the sum of
 
* the <tt>HashSet</tt> instance's size (the number of elements) plus the
 
* "capacity" of the backing <tt>HashMap</tt> 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.
 
*
 
* <p><strong>Note that this implementation is not synchronized.</strong>
 
* If multiple threads access a hash set concurrently, and at least one of
 
* the threads modifies the set, it <i>must</i> 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
 
* {@link Collections#synchronizedSet Collections.synchronizedSet}
 
* method.
  
This is best done at creation time, to prevent accidental
 
* unsynchronized access to the set:<pre>
 
*
   
Set s = Collections.synchronizedSet(new HashSet(...));</pre>
 
*
 
* <p>The iterators returned by this class's <tt>iterator</tt> method are
 
* <i>fail-fast</i>: if the set is modified at any time after the iterator is
 
* created, in any way except through the iterator's own <tt>remove</tt>
 
* method, the Iterator throws a {@link 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.
 
*
 
* <p>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 <tt>ConcurrentModificationException</tt> on a best-effort basis.
 
* Therefore, it would be wrong to write a program that depended on this
 
* exception for its correctness: <i>the fail-fast behavior of iterators
 
* should be used only to detect bugs.</i>
 
*
 
* <p>This class is a member of the
 
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
 
* Java Collections Framework</a>.
 
*
 
* @param <E> the type of elements maintained by this set
 
*
 
* @author
  
Josh Bloch
 
* @author
  
Neal Gafter
 
* @see
     
Collection
 
* @see
     
Set
 
* @see
     
TreeSet
 
* @see
     
HashMap
 
* @since
   
1.2
 
*/


public class HashSet<E>
    
extends AbstractSet<E>
    
implements Set<E>, Cloneable, java.io.Serializable
{
    
static final long serialVersionUID = -5024744406713321676L;

    
private transient HashMap<E,Object> map;

    
// Dummy value to associate with an Object in the backing Map
    
private static final Object PRESENT = new Object();

    
/**
     
* Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     
* default initial capacity (16) and load factor (0.75).
     
*/

    
public HashSet() {
        
map = new HashMap<>();
    
}

    
/**
     
* Constructs a new set containing the elements in the specified
     
* collection.
  
The <tt>HashMap</tt> 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<? extends E> c) {
        
map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
        
addAll(c);
    
}

    
/**
     
* Constructs a new, empty set; the backing <tt>HashMap</tt> 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
     
* @throwsIllegalArgumentException if the initial capacity is less
     
*
             
than zero, or if the load factor is nonpositive
     
*/

    
public HashSet(int initialCapacity, float loadFactor) {
        
map = new HashMap<>(initialCapacity, loadFactor);
    
}

    
/**
     
* Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     
* the specified initial capacity and default load factor (0.75).
     
*
     
* @param
      
initialCapacity
   
the initial capacity of the hash table
     
* @throwsIllegalArgumentException if the initial capacity is less
     
*
             
than zero
     
*/

    
public HashSet(int initialCapacity) {
        
map = new HashMap<>(initialCapacity);
    
}

    
/**
     
* Constructs a new, empty linked hash set.
  
(This package private
     
* constructor is only used by LinkedHashSet.) The backing
     
* HashMap instance is a LinkedHashMap with 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
     
* @param
      
dummy
             
ignored (distinguishes this
     
*
             
constructor from other int, float constructor.)
     
* @throwsIllegalArgumentException if the initial capacity is less
     
*
             
than zero, or if the load factor is nonpositive
     
*/

    
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        
map = new LinkedHashMap<>(initialCapacity, loadFactor);
    
}

    
/**
     
* 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<E> iterator() {
        
return map.keySet().iterator();
    
}

    
/**
     
* Returns the number of elements in this set (its cardinality).
     
*
     
* @return the number of elements in this set (its cardinality)
     
*/

    
public int size() {
        
return map.size();
    
}

    
/**
     
* Returns <tt>true</tt> if this set contains no elements.
     
*
     
* @return <tt>true</tt> if this set contains no elements
     
*/

    
public boolean isEmpty() {
        
return map.isEmpty();
    
}

    
/**
     
* Returns <tt>true</tt> if this set contains the specified element.
     
* More formally, returns <tt>true</tt> if and only if this set
     
* contains an element <tt>e</tt> such that
     
* <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     
*
     
* @param o element whose presence in this set is to be tested
     
* @return <tt>true</tt> if this set contains the specified element
     
*/

    
public boolean contains(Object o) {
        
return map.containsKey(o);
    
}

    
/**
     
* Adds the specified element to this set if it is not already present.
     
* More formally, adds the specified element <tt>e</tt> to this set if
     
* this set contains no element <tt>e2</tt> such that
     
* <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
     
* If this set already contains the element, the call leaves the set
     
* unchanged and returns <tt>false</tt>.
     
*
     
* @param e element to be added to this set
     
* @return <tt>true</tt> if this set did not already contain the specified
     
* element
     
*/

    
public boolean add(E e) {
        
return map.put(e, PRESENT)==null;
    
}

    
/**
     
* Removes the specified element from this set if it is present.
     
* More formally, removes an element <tt>e</tt> such that
     
* <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     
* if this set contains such an element.
  
Returns <tt>true</tt> if
     
* this set contained the element (or equivalently, if this set
     
* changed as a result of the call).
  
(This set will not contain the
     
* element once the call returns.)
     
*
     
* @param o object to be removed from this set, if present
     
* @return <tt>true</tt> if the set contained the specified element
     
*/

    
public boolean remove(Object o) {
        
return map.remove(o)==PRESENT;
    
}

    
/**
     
* Removes all of the elements from this set.
     
* The set will be empty after this call returns.
     
*/

    
public void clear() {
        
map.clear();
    
}

    
/**
     
* Returns a shallow copy of this <tt>HashSet</tt> instance: the elements
     
* themselves are not cloned.
     
*
     
* @return a shallow copy of this set
     
*/

    
@SuppressWarnings("unchecked")
    
public Object clone() {
        
try {
            
HashSet<E> newSet = (HashSet<E>) super.clone();
            
newSet.map = (HashMap<E, Object>) map.clone();
            
return newSet;
        
} catch (CloneNotSupportedException e) {
            
throw new InternalError(e);
        
}
    
}

    
/**
     
* Save the state of this <tt>HashSet</tt> instance to a stream (that is,
     
* serialize it).
     
*
     
* @serialData The capacity of the backing <tt>HashMap</tt> 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 {
        
// Write out any hidden serialization magic
        
s.defaultWriteObject();

        
// Write out HashMap capacity and load factor
        
s.writeInt(map.capacity());
        
s.writeFloat(map.loadFactor());

        
// Write out size
        
s.writeInt(map.size());

        
// Write out all elements in the proper order.
        
for (E e : map.keySet())
            
s.writeObject(e);
    
}

    
/**
     
* Reconstitute the <tt>HashSet</tt> instance from a stream (that is,
     
* deserialize it).
     
*/

    
private void readObject(java.io.ObjectInputStream s)
        
throws java.io.IOException, ClassNotFoundException {
        
// Read in any hidden serialization magic
        
s.defaultReadObject();

        
// Read capacity and verify non-negative.
        
int capacity = s.readInt();
        
if (capacity < 0) {
            
throw new InvalidObjectException("Illegal capacity: " +
                                             
capacity);
        
}

        
// Read load factor and verify positive and non NaN.
        
float loadFactor = s.readFloat();
        
if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
            
throw new InvalidObjectException("Illegal load factor: " +
                                             
loadFactor);
        
}

        
// Read size and verify non-negative.
        
int size = s.readInt();
        
if (size < 0) {
            
throw new InvalidObjectException("Illegal size: " +
                                             
size);
        
}
        
// Set the capacity according to the size and load factor ensuring that
        
// the HashMap is at least 25% full but clamping to maximum capacity.
        
capacity = (int) Math.min(size * Math.min(1 / loadFactor, 4.0f),
                
HashMap.MAXIMUM_CAPACITY);

        
// Constructing the backing map will lazily create an array when the first element is
        
// added, so check it before construction. Call HashMap.tableSizeFor to compute the
        
// actual allocation size. Check Map.Entry[].class since it's the nearest public type to
        
// what is actually created.

        
SharedSecrets.getJavaOISAccess()
                     
.checkArray(s, Map.Entry[].class, HashMap.tableSizeFor(capacity));

        
// Create backing HashMap
        
map = (((HashSet<?>)this) instanceof LinkedHashSet ?
               
new LinkedHashMap<E,Object>(capacity, loadFactor) :
               
new HashMap<E,Object>(capacity, loadFactor));

        
// Read in all elements in the proper order.
        
for (int i=0; i<size; i++) {
            
@SuppressWarnings("unchecked")
                
E e = (E) s.readObject();
            
map.put(e, PRESENT);
        
}
    
}

    
/**
     
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
     
* and <em>fail-fast</em> {@link Spliterator} over the elements in this
     
* set.
     
*
     
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
     
* {@link Spliterator#DISTINCT}.
  
Overriding implementations should document
     
* the reporting of additional characteristic values.
     
*
     
* @return a {@code Spliterator} over the elements in this set
     
* @since 1.8
     
*/

    
public Spliterator<E> spliterator() {
        
return new HashMap.KeySpliterator<E,Object>(map, 0, -1, 0, 0);
    
}
}