MultivaluedHashMap.java
/*
* Copyright (c) 2012, 2017 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package org.glassfish.tyrus.core.uri.internal;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* A hash table based implementation of {@link MultivaluedMap} interface.
* <p>
* This implementation provides all of the optional map operations. This class
* makes no guarantees as to the order of the map; in particular, it does not
* guarantee that the order will remain constant over time. The implementation
* permits {@code null} key. By default the implementation does also permit
* {@code null} values, but ignores them. This behavior can be customized
* by overriding the protected {@link #addNull(List) addNull(...)} and
* {@link #addFirstNull(List) addFirstNull(...)} methods.
* <p>
* This implementation provides constant-time performance for the basic
* operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function
* disperses the elements properly among the buckets. Iteration over
* collection views requires time proportional to the "capacity" of the
* map instance (the number of buckets) plus its size (the number
* of key-value mappings). 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>
* An instance of <tt>MultivaluedHashMap</tt> has two parameters that affect its
* performance: <i>initial capacity</i> and <i>load factor</i>. The <i>capacity</i>
* is the number of buckets in the hash table, and the initial capacity is simply
* the capacity at the time the hash table is created. The <i>load factor</i> is
* a measure of how full the hash table is allowed to get before its capacity is
* automatically increased. When the number of entries in the hash table exceeds
* the product of the load factor and the current capacity, the hash table is
* <i>rehashed</i> (that is, internal data structures are rebuilt) so that the
* hash table has approximately twice the number of buckets.
* <p>
* As a general rule, the default load factor (.75) offers a good tradeoff
* between time and space costs. Higher values decrease the space overhead
* but increase the lookup cost (reflected in most of the operations of the
* <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>). The
* expected number of entries in the map and its load factor should be taken
* into account when setting its initial capacity, so as to minimize the
* number of rehash operations. If the initial capacity is greater
* than the maximum number of entries divided by the load factor, no
* rehash operations will ever occur.
* <p>
* If many mappings are to be stored in a <tt>MultivaluedHashMap</tt> instance,
* creating it with a sufficiently large capacity will allow the mappings to
* be stored more efficiently than letting it perform automatic rehashing as
* needed to grow the table.
* <p>
* <strong>Note that this implementation is not guaranteed to be synchronized.</strong>
* If multiple threads access a hash map concurrently, and at least one of
* the threads modifies the map structurally, it <i>must</i> be
* synchronized externally. (A structural modification is any operation
* that adds or deletes one or more mappings; merely changing the value
* associated with a key that an instance already contains is not a
* structural modification.) This is typically accomplished by
* synchronizing on some object that naturally encapsulates the map.
* <p>
* The iterators returned by all of this class's "collection view methods"
* are <i>fail-fast</i>: if the map is structurally modified at any time after
* the iterator is created, in any way except through the iterator's own
* <tt>remove</tt> method, the iterator will throw a {@link java.util.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>
*
* @param <K> the type of keys maintained by this map.
* @param <V> the type of mapped values.
* @author Paul Sandoz
* @author Marek Potociar
* @since 2.0
*/
public class MultivaluedHashMap<K, V> extends AbstractMultivaluedMap<K, V> implements Serializable {
private static final long serialVersionUID = -6052320403766368902L;
/**
* Constructs an empty multivalued hash map with the default initial capacity
* ({@code 16}) and the default load factor ({@code 0.75}).
*/
public MultivaluedHashMap() {
super(new HashMap<K, List<V>>());
}
/**
* Constructs an empty multivalued hash map with the specified initial
* capacity and the default load factor ({@code 0.75}).
*
* @param initialCapacity the initial capacity.
* @throws IllegalArgumentException if the initial capacity is negative.
*/
public MultivaluedHashMap(int initialCapacity) {
super(new HashMap<K, List<V>>(initialCapacity));
}
/**
* Constructs an empty multivalued hash map with the specified initial
* capacity and load factor.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @throws IllegalArgumentException if the initial capacity is negative
* or the load factor is nonpositive
*/
public MultivaluedHashMap(int initialCapacity, float loadFactor) {
super(new HashMap<K, List<V>>(initialCapacity, loadFactor));
}
/**
* Constructs a new multivalued hash map with the same mappings as the
* specified {@link MultivaluedMap }. The {@link List} instances holding
* the values of each key are created anew instead of being reused.
*
* @param map the multivalued map whose mappings are to be placed in this
* multivalued map.
* @throws NullPointerException if the specified map is {@code null}
*/
public MultivaluedHashMap(MultivaluedMap<? extends K, ? extends V> map) {
this();
putAll(map);
}
/**
* This private method is used by the copy constructor to avoid exposing
* additional generic parameters through the public API documentation.
*
* @param <T> any subclass of K
* @param <U> any subclass of V
* @param map the map
*/
private <T extends K, U extends V> void putAll(MultivaluedMap<T, U> map) {
for (Entry<T, List<U>> e : map.entrySet()) {
store.put(e.getKey(), new ArrayList<V>(e.getValue()));
}
}
/**
* Constructs a new multivalued hash map with the same mappings as the
* specified single-valued {@link Map }.
*
* @param map the single-valued map whose mappings are to be placed in this
* multivalued map.
* @throws NullPointerException if the specified map is {@code null}
*/
public MultivaluedHashMap(Map<? extends K, ? extends V> map) {
this();
for (Entry<? extends K, ? extends V> e : map.entrySet()) {
this.putSingle(e.getKey(), e.getValue());
}
}
}