mssql.googlecode.concurrentlinkedhashmap.Weighers Maven / Gradle / Ivy
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/*
* Copyright 2010 Google Inc. All Rights Reserved.
*
* 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 mssql.googlecode.concurrentlinkedhashmap;
import static mssql.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap.checkNotNull;
import java.io.Serializable;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A common set of {@link Weigher} and {@link EntryWeigher} implementations.
*
* @author [email protected] (Ben Manes)
* @see
* http://code.google.com/p/concurrentlinkedhashmap/
*/
public final class Weighers {
private Weighers() {
throw new AssertionError();
}
/**
* A entry weigher backed by the specified weigher. The weight of the value
* determines the weight of the entry.
*
* @param K
* @param V
* @param weigher the weigher to be "wrapped" in a entry weigher.
* @return A entry weigher view of the specified weigher.
*/
public static EntryWeigher asEntryWeigher(
final Weigher weigher) {
return (weigher == singleton())
? Weighers.entrySingleton()
: new EntryWeigherView(weigher);
}
/**
* A weigher where an entry has a weight of 1. A map bounded with
* this weigher will evict when the number of key-value pairs exceeds the
* capacity.
*
* @param K
* @param V
* @return A weigher where a value takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static EntryWeigher entrySingleton() {
return (EntryWeigher) SingletonEntryWeigher.INSTANCE;
}
/**
* 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.
*
* @param V
* @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.
*
* @param E
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> iterable() {
return (Weigher>) (Weigher) IterableWeigher.INSTANCE;
}
/**
* 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.
*
* @param E
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> collection() {
return (Weigher>) (Weigher) CollectionWeigher.INSTANCE;
}
/**
* 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.
*
* @param E
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> list() {
return (Weigher>) (Weigher) ListWeigher.INSTANCE;
}
/**
* 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.
*
* @param E
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> set() {
return (Weigher>) (Weigher) SetWeigher.INSTANCE;
}
/**
* 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.
*
* @param A
* @param B
* @return A weigher where each entry takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static Weigher> map() {
return (Weigher>) (Weigher) MapWeigher.INSTANCE;
}
static final class EntryWeigherView implements EntryWeigher, Serializable {
static final long serialVersionUID = 1;
final Weigher weigher;
EntryWeigherView(Weigher weigher) {
checkNotNull(weigher);
this.weigher = weigher;
}
@Override
public int weightOf(K key, V value) {
return weigher.weightOf(value);
}
}
enum SingletonEntryWeigher implements EntryWeigher {
INSTANCE;
@Override
public int weightOf(Object key, Object value) {
return 1;
}
}
enum SingletonWeigher implements Weigher