com.google.gwt.dev.util.collect.Sets 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.Collection;
import java.util.Collections;
import java.util.Set;
/**
* Utility methods for operating on memory-efficient sets. All sets of size 0 or
* 1 are assumed to be immutable. All sets of size greater than 1 are assumed to
* be mutable.
*/
public class Sets {
private static final Class MULTI_SET_CLASS = HashSet.class;
private static final Class SINGLETON_SET_CLASS = Collections.singleton(
null).getClass();
public static Set add(Set set, T toAdd) {
switch (set.size()) {
case 0:
// Empty -> Singleton
return create(toAdd);
case 1: {
if (set.contains(toAdd)) {
return set;
}
// Singleton -> HashSet
Set result = new HashSet();
result.add(set.iterator().next());
result.add(toAdd);
return result;
}
default:
// HashSet
set.add(toAdd);
return set;
}
}
public static Set addAll(Set set, Collection toAdd) {
switch (toAdd.size()) {
case 0:
return set;
case 1:
return add(set, toAdd.iterator().next());
}
switch (set.size()) {
case 0:
// Empty -> HashSet
return new HashSet(toAdd);
case 1: {
// Singleton -> HashSet
Set result = new HashSet();
result.add(set.iterator().next());
result.addAll(toAdd);
return result;
}
default:
// HashSet
set.addAll(toAdd);
return set;
}
}
public static Set create() {
return Collections.emptySet();
}
public static Set create(T item) {
return Collections.singleton(item);
}
public static Set create(T... items) {
switch (items.length) {
case 0:
return create();
case 1:
return create(items[0]);
default:
HashSet result = new HashSet();
result.addAll(items);
return result;
}
}
public static Set normalize(Set set) {
switch (set.size()) {
case 0:
return create();
case 1: {
if (set.getClass() == SINGLETON_SET_CLASS) {
return set;
}
return create(set.iterator().next());
}
default:
if (set.getClass() == MULTI_SET_CLASS) {
return set;
}
HashSet result = new HashSet();
result.addAll(set);
return result;
}
}
public static Set normalizeUnmodifiable(Set set) {
if (set.size() < 2) {
return normalize(set);
} else {
// TODO: implement an UnmodifiableHashSet?
return Collections.unmodifiableSet(normalize(set));
}
}
public static Set remove(Set set, T toRemove) {
switch (set.size()) {
case 0:
// Empty
return set;
case 1:
// Singleton -> Empty
if (set.contains(toRemove)) {
return create();
}
return set;
case 2:
// HashSet -> Singleton
if (set.remove(toRemove)) {
return create(set.iterator().next());
}
return set;
default:
// HashSet
set.remove(toRemove);
return set;
}
}
}