|
Java example source code file (HashSet.java)
The HashSet.java Java example source code/* * Copyright (c) 1997, 2013, 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; /** * This class implements the <tt>Set interface, backed by a hash table * (actually a <tt>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 <tt>null * element. * * <p>This class offers constant time performance for the basic operations * (<tt>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 <tt>HashSet instance's size (the number of elements) plus the * "capacity" of the backing <tt>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. * * <p>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 <i>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 * {@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 iterator method are * <i>fail-fast: if the set is modified at any time after the iterator is * created, in any way except through the iterator's own <tt>remove * 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 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 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 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 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) { map = new HashMap<>(initialCapacity, loadFactor); } /** * Constructs a new, empty set; the backing <tt>HashMap instance has * the specified initial capacity and default load factor (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) { 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.) * @throws IllegalArgumentException 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 if this set contains no elements. * * @return <tt>true if this set contains no elements */ public boolean isEmpty() { return map.isEmpty(); } /** * Returns <tt>true if this set contains the specified element. * More formally, returns <tt>true if and only if this set * contains an element <tt>e such that * <tt>(o==null ? e==null : o.equals(e)). * * @param o element whose presence in this set is to be tested * @return <tt>true 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 to this set if * this set contains no element <tt>e2 such that * <tt>(e==null ? e2==null : e.equals(e2)). * If this set already contains the element, the call leaves the set * unchanged and returns <tt>false. * * @param e element to be added to this set * @return <tt>true 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 such that * <tt>(o==null ? e==null : o.equals(e)), * if this set contains such an element. Returns <tt>true 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 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 instance: the elements * themselves are not cloned. * * @return a shallow copy of this set */ @SuppressWarnings("unchecked") public Object clone() { try { HashSet<E> newSet = (HashSet Other Java examples (source code examples)Here is a short list of links related to this Java HashSet.java source code file: |
... this post is sponsored by my books ... | |
#1 New Release! |
FP Best Seller |
Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.
A percentage of advertising revenue from
pages under the /java/jwarehouse
URI on this website is
paid back to open source projects.