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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/util/HashSet.java
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+/* HashSet.java -- a class providing a HashMap-backed Set
+ Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING. If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.util;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+
+/**
+ * This class provides a HashMap-backed implementation of the Set interface.
+ * <p>
+ *
+ * Most operations are O(1), assuming no hash collisions. In the worst
+ * case (where all hashes collide), operations are O(n). Setting the
+ * initial capacity too low will force many resizing operations, but
+ * setting the initial capacity too high (or loadfactor too low) leads
+ * to wasted memory and slower iteration.
+ * <p>
+ *
+ * HashSet accepts the null key and null values. It is not synchronized,
+ * so if you need multi-threaded access, consider using:<br>
+ * <code>Set s = Collections.synchronizedSet(new HashSet(...));</code>
+ * <p>
+ *
+ * The iterators are <i>fail-fast</i>, meaning that any structural
+ * modification, except for <code>remove()</code> called on the iterator
+ * itself, cause the iterator to throw a
+ * {@link ConcurrentModificationException} rather than exhibit
+ * non-deterministic behavior.
+ *
+ * @author Jon Zeppieri
+ * @author Eric Blake (ebb9@email.byu.edu)
+ * @see Collection
+ * @see Set
+ * @see TreeSet
+ * @see Collections#synchronizedSet(Set)
+ * @see HashMap
+ * @see LinkedHashSet
+ * @since 1.2
+ * @status updated to 1.4
+ */
+public class HashSet<T> extends AbstractSet<T>
+ implements Set<T>, Cloneable, Serializable
+{
+ /**
+ * Compatible with JDK 1.2.
+ */
+ private static final long serialVersionUID = -5024744406713321676L;
+
+ /**
+ * The HashMap which backs this Set.
+ */
+ private transient HashMap<T, String> map;
+
+ /**
+ * Construct a new, empty HashSet whose backing HashMap has the default
+ * capacity (11) and loadFacor (0.75).
+ */
+ public HashSet()
+ {
+ this(HashMap.DEFAULT_CAPACITY, HashMap.DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Construct a new, empty HashSet whose backing HashMap has the supplied
+ * capacity and the default load factor (0.75).
+ *
+ * @param initialCapacity the initial capacity of the backing HashMap
+ * @throws IllegalArgumentException if the capacity is negative
+ */
+ public HashSet(int initialCapacity)
+ {
+ this(initialCapacity, HashMap.DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Construct a new, empty HashSet whose backing HashMap has the supplied
+ * capacity and load factor.
+ *
+ * @param initialCapacity the initial capacity of the backing HashMap
+ * @param loadFactor the load factor of the backing HashMap
+ * @throws IllegalArgumentException if either argument is negative, or
+ * if loadFactor is POSITIVE_INFINITY or NaN
+ */
+ public HashSet(int initialCapacity, float loadFactor)
+ {
+ map = init(initialCapacity, loadFactor);
+ }
+
+ /**
+ * Construct a new HashSet with the same elements as are in the supplied
+ * collection (eliminating any duplicates, of course). The backing storage
+ * has twice the size of the collection, or the default size of 11,
+ * whichever is greater; and the default load factor (0.75).
+ *
+ * @param c a collection of initial set elements
+ * @throws NullPointerException if c is null
+ */
+ public HashSet(Collection<? extends T> c)
+ {
+ this(Math.max(2 * c.size(), HashMap.DEFAULT_CAPACITY));
+ addAll(c);
+ }
+
+ /**
+ * Adds the given Object to the set if it is not already in the Set.
+ * This set permits a null element.
+ *
+ * @param o the Object to add to this Set
+ * @return true if the set did not already contain o
+ */
+ public boolean add(T o)
+ {
+ return map.put(o, "") == null;
+ }
+
+ /**
+ * Empties this Set of all elements; this takes constant time.
+ */
+ public void clear()
+ {
+ map.clear();
+ }
+
+ /**
+ * Returns a shallow copy of this Set. The Set itself is cloned; its
+ * elements are not.
+ *
+ * @return a shallow clone of the set
+ */
+ public Object clone()
+ {
+ HashSet<T> copy = null;
+ try
+ {
+ copy = (HashSet<T>) super.clone();
+ }
+ catch (CloneNotSupportedException x)
+ {
+ // Impossible to get here.
+ }
+ copy.map = (HashMap<T, String>) map.clone();
+ return copy;
+ }
+
+ /**
+ * Returns true if the supplied element is in this Set.
+ *
+ * @param o the Object to look for
+ * @return true if it is in the set
+ */
+ public boolean contains(Object o)
+ {
+ return map.containsKey(o);
+ }
+
+ /**
+ * Returns true if this set has no elements in it.
+ *
+ * @return <code>size() == 0</code>.
+ */
+ public boolean isEmpty()
+ {
+ return map.size == 0;
+ }
+
+ /**
+ * Returns an Iterator over the elements of this Set, which visits the
+ * elements in no particular order. For this class, the Iterator allows
+ * removal of elements. The iterator is fail-fast, and will throw a
+ * ConcurrentModificationException if the set is modified externally.
+ *
+ * @return a set iterator
+ * @see ConcurrentModificationException
+ */
+ public Iterator<T> iterator()
+ {
+ // Avoid creating intermediate keySet() object by using non-public API.
+ return map.iterator(HashMap.KEYS);
+ }
+
+ /**
+ * Removes the supplied Object from this Set if it is in the Set.
+ *
+ * @param o the object to remove
+ * @return true if an element was removed
+ */
+ public boolean remove(Object o)
+ {
+ return (map.remove(o) != null);
+ }
+
+ /**
+ * Returns the number of elements in this Set (its cardinality).
+ *
+ * @return the size of the set
+ */
+ public int size()
+ {
+ return map.size;
+ }
+
+ /**
+ * Helper method which initializes the backing Map. Overridden by
+ * LinkedHashSet for correct semantics.
+ *
+ * @param capacity the initial capacity
+ * @param load the initial load factor
+ * @return the backing HashMap
+ */
+ HashMap init(int capacity, float load)
+ {
+ return new HashMap(capacity, load);
+ }
+
+ /**
+ * Serializes this object to the given stream.
+ *
+ * @param s the stream to write to
+ * @throws IOException if the underlying stream fails
+ * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float)
+ * of the backing store, followed by the set size (int),
+ * then a listing of its elements (Object) in no order
+ */
+ private void writeObject(ObjectOutputStream s) throws IOException
+ {
+ s.defaultWriteObject();
+ // Avoid creating intermediate keySet() object by using non-public API.
+ Iterator<T> it = map.iterator(HashMap.KEYS);
+ s.writeInt(map.buckets.length);
+ s.writeFloat(map.loadFactor);
+ s.writeInt(map.size);
+ while (it.hasNext())
+ s.writeObject(it.next());
+ }
+
+ /**
+ * Deserializes this object from the given stream.
+ *
+ * @param s the stream to read from
+ * @throws ClassNotFoundException if the underlying stream fails
+ * @throws IOException if the underlying stream fails
+ * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float)
+ * of the backing store, followed by the set size (int),
+ * then a listing of its elements (Object) in no order
+ */
+ private void readObject(ObjectInputStream s)
+ throws IOException, ClassNotFoundException
+ {
+ s.defaultReadObject();
+
+ map = init(s.readInt(), s.readFloat());
+ for (int size = s.readInt(); size > 0; size--)
+ map.put((T) s.readObject(), "");
+ }
+}