com.twelvemonkeys.util.NullMap Maven / Gradle / Ivy
/*
* 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}).
*
* 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 Harald Kuhr
* @version $Id: com/twelvemonkeys/util/NullMap.java#2 $
*/
public final class NullMap implements Map, 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 values() {
return Collections.emptyList();
}
public final void putAll(Map pMap) {
}
public final Set> entrySet() {
return Collections.emptySet();
}
public final Set 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;
}
}