/*
* Copyright (c) 2008, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.twelvemonkeys.util;
import java.io.
Serializable;
import java.util.
Collection;
import java.util.
Collections;
import java.util.
Map;
import java.util.
Set;
/**
* An (immutable) empty {@link Map}, that supports all {@code Map} operations
* without throwing exceptions (in contrast to {@link Collections#EMPTY_MAP}
* that will throw exceptions on {@code put}/{@code remove}).
* <p/>
* NOTE: This is not a general purpose {@code Map} implementation,
* as the {@code put} and {@code putAll} methods will not modify the map.
* Instances of this class will always be an empty map.
*
* @author <a href="mailto:harald.kuhr@gmail.com">Harald Kuhr</a>
* @version $Id: com/twelvemonkeys/util/NullMap.java#2 $
*/
public final class
NullMap<K, V> implements
Map<K, V>,
Serializable {
public final int
size() {
return 0;
}
public final void
clear() {
}
public final boolean
isEmpty() {
return true;
}
public final boolean
containsKey(
Object pKey) {
return false;
}
public final boolean
containsValue(
Object pValue) {
return false;
}
public final
Collection<V>
values() {
return
Collections.
emptyList();
}
public final void
putAll(
Map pMap) {
}
public final
Set<
Entry<K, V>>
entrySet() {
return
Collections.
emptySet();
}
public final
Set<K>
keySet() {
return
Collections.
emptySet();
}
public final V
get(
Object pKey) {
return null;
}
public final V
remove(
Object pKey) {
return null;
}
public final V
put(
Object pKey,
Object pValue) {
return null;
}
/**
* Tests the given object for equality (wether it is also an empty
* {@code Map}).
* This is consistent with the standard {@code Map} implementations of the
* Java Collections Framework.
*
* @param pOther the object to compare with
* @return {@code true} if {@code pOther} is an empty {@code Map},
* otherwise {@code false}
*/
public boolean
equals(
Object pOther) {
return (
pOther instanceof
Map) && ((
Map)
pOther).
isEmpty();
}
/**
* Returns the {@code hashCode} of the empty map, {@code 0}.
* This is consistent with the standard {@code Map} implementations of the
* Java Collections Framework.
*
* @return {@code 0}, always
*/
public int
hashCode() {
return 0;
}
}