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/*
* Copyright 2010 Benjamin Manes
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.googlecode.concurrentlinkedhashmap;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A common set of {@link Weigher} implementations.
*
* @author [email protected] (Ben Manes)
* @see http://code.google.com/p/concurrentlinkedhashmap/
*/
public final class Weighers {
private Weighers() {
throw new AssertionError();
}
/**
* A weigher where a value has a weight of 1. A map bounded with
* this weigher will evict when the number of key-value pairs exceeds the
* capacity.
*
* @return A weigher where a value takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher singleton() {
return (Weigher) SingletonWeigher.INSTANCE;
}
/**
* A weigher where the value is a byte array and its weight is the number of
* bytes. A map bounded with this weigher will evict when the number of bytes
* exceeds the capacity rather than the number of key-value pairs in the map.
* This allows for restricting the capacity based on the memory-consumption
* and is primarily for usage by dedicated caching servers that hold the
* serialized data.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each byte takes one unit of capacity.
*/
public static Weigher byteArray() {
return ByteArrayWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Iterable} and its weight is the
* number of elements. This weigher only should be used when the alternative
* {@link #collection()} weigher cannot be, as evaluation takes O(n) time. A
* map bounded with this weigher will evict when the total number of elements
* exceeds the capacity rather than the number of key-value pairs in the map.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> iterable() {
Weigher weigher = IterableWeigher.INSTANCE;
return (Weigher>) weigher;
}
/**
* A weigher where the value is a {@link Collection} and its weight is the
* number of elements. A map bounded with this weigher will evict when the
* total number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> collection() {
Weigher weigher = CollectionWeigher.INSTANCE;
return (Weigher>) weigher;
}
/**
* A weigher where the value is a {@link List} and its weight is the number
* of elements. A map bounded with this weigher will evict when the total
* number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> list() {
Weigher weigher = ListWeigher.INSTANCE;
return (Weigher>) weigher;
}
/**
* A weigher where the value is a {@link Set} and its weight is the number
* of elements. A map bounded with this weigher will evict when the total
* number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> set() {
Weigher weigher = SetWeigher.INSTANCE;
return (Weigher>) weigher;
}
/**
* A weigher where the value is a {@link Map} and its weight is the number of
* entries. A map bounded with this weigher will evict when the total number of
* entries across all values exceeds the capacity rather than the number of
* key-value pairs in the map.
*
* A value with a weight of 0 will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each entry takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> map() {
Weigher weigher = MapWeigher.INSTANCE;
return (Weigher>) weigher;
}
private enum SingletonWeigher implements Weigher