com.google.gwt.dev.util.collect.IdentityMaps Maven / Gradle / Ivy
/*
* Copyright 2009 Google Inc.
*
* 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.google.gwt.dev.util.collect;
import java.util.Collections;
import java.util.Map;
/**
* Utility methods for operating on memory-efficient maps. All maps of size 0 or
* 1 are assumed to be immutable. All maps of size greater than 1 are assumed to
* be mutable.
*/
public class IdentityMaps {
private static final Class MULTI_MAP_CLASS = IdentityHashMap.class;
private static final Class SINGLETON_MAP_CLASS = IdentitySingletonMap.class;
public static Map create() {
return Collections.emptyMap();
}
public static Map create(K key, V value) {
return new IdentitySingletonMap(key, value);
}
public static Map normalize(Map map) {
switch (map.size()) {
case 0:
return create();
case 1: {
if (map.getClass() == SINGLETON_MAP_CLASS) {
return map;
}
K key = map.keySet().iterator().next();
return create(key, map.get(key));
}
default:
if (map.getClass() == MULTI_MAP_CLASS) {
return map;
}
return new IdentityHashMap(map);
}
}
public static Map normalizeUnmodifiable(Map map) {
if (map.size() < 2) {
return normalize(map);
} else {
// TODO: implement an UnmodifiableIdentityHashMap?
return Collections.unmodifiableMap(normalize(map));
}
}
}