com.google.inject.internal.util.Sets Maven / Gradle / Ivy
/*
* Copyright (C) 2007 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.inject.internal.util;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
/**
* Static utility methods pertaining to {@link Set} instances. Also see this
* class's counterparts {@link Lists} and {@link Maps}.
*
* @author Kevin Bourrillion
* @author Jared Levy
*/
public final class Sets {
private Sets() {}
// HashSet
/**
* Creates an empty {@code HashSet} instance.
*
* Note: if {@code E} is an {@link Enum} type, use {@link
* EnumSet#noneOf} instead.
*
*
Note: if you need an immutable empty Set, use {@link
* Collections#emptySet} instead.
*
* @return a newly created, empty {@code HashSet}
*/
public static HashSet newHashSet() {
return new HashSet();
}
// TODO: Modify the sets returned by newConcurrentHashSet so calling
// remove(null) on them doesn't throw an NPE.
// LinkedHashSet
/**
* Creates an empty {@code LinkedHashSet} instance.
*
* @return a newly created, empty {@code LinkedHashSet}
*/
public static LinkedHashSet newLinkedHashSet() {
return new LinkedHashSet();
}
/*
* Regarding newSetForMap() and SetFromMap:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
/**
* Returns a set backed by the specified map. The resulting set displays
* the same ordering, concurrency, and performance characteristics as the
* backing map. In essence, this factory method provides a {@link Set}
* implementation corresponding to any {@link Map} implementation. There is no
* need to use this method on a {@link Map} implementation that already has a
* corresponding {@link Set} implementation (such as {@link HashMap} or
* {@link TreeMap}).
*
* Each method invocation on the set returned by this method results in
* exactly one method invocation on the backing map or its keySet
* view, with one exception. The addAll method is implemented as a
* sequence of put invocations on the backing map.
*
*
The specified map must be empty at the time this method is invoked,
* and should not be accessed directly after this method returns. These
* conditions are ensured if the map is created empty, passed directly
* to this method, and no reference to the map is retained, as illustrated
* in the following code fragment:
*
* Set<Object> identityHashSet = Sets.newSetFromMap(
* new IdentityHashMap<Object, Boolean>());
*
* This method has the same behavior as the JDK 6 method
* {@code Collections.newSetFromMap()}. The returned set is serializable if
* the backing map is.
*
* @param map the backing map
* @return the set backed by the map
* @throws IllegalArgumentException if map is not empty
*/
public static Set newSetFromMap(Map map) {
return new SetFromMap(map);
}
private static class SetFromMap extends AbstractSet
implements Set, Serializable {
private final Map m; // The backing map
private transient Set s; // Its keySet
SetFromMap(Map map) {
Preconditions.checkArgument(map.isEmpty(), "Map is non-empty");
m = map;
s = map.keySet();
}
@Override public void clear() {
m.clear();
}
@Override public int size() {
return m.size();
}
@Override public boolean isEmpty() {
return m.isEmpty();
}
@Override public boolean contains(Object o) {
return m.containsKey(o);
}
@Override public boolean remove(Object o) {
return m.remove(o) != null;
}
@Override public boolean add(E e) {
return m.put(e, Boolean.TRUE) == null;
}
@Override public Iterator iterator() {
return s.iterator();
}
@Override public Object[] toArray() {
return s.toArray();
}
@Override public T[] toArray(T[] a) {
return s.toArray(a);
}
@Override public String toString() {
return s.toString();
}
@Override public int hashCode() {
return s.hashCode();
}
@Override public boolean equals(@Nullable Object object) {
return this == object || this.s.equals(object);
}
@Override public boolean containsAll(Collection c) {
return s.containsAll(c);
}
@Override public boolean removeAll(Collection c) {
return s.removeAll(c);
}
@Override public boolean retainAll(Collection c) {
return s.retainAll(c);
}
// addAll is the only inherited implementation
static final long serialVersionUID = 0;
private void readObject(ObjectInputStream stream)
throws IOException, ClassNotFoundException {
stream.defaultReadObject();
s = m.keySet();
}
}
/**
* Calculates and returns the hash code of {@code s}.
*/
static int hashCodeImpl(Set s) {
int hashCode = 0;
for (Object o : s) {
hashCode += o != null ? o.hashCode() : 0;
}
return hashCode;
}
}