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/*
* Copyright (C) 2008 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.common.collect;
import com.google.common.base.Function;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.base.Nullable;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
/**
* Provides static methods for working with {@code Collection} instances.
*
* @author Chris Povirk
* @author Mike Bostock
* @author Jared Levy
*/
public final class Collections2 {
private Collections2() {}
/**
* Returns {@code true} if the collection {@code self} contains all of the
* elements in the collection {@code c}.
*
* This method iterates over the specified collection {@code c}, checking
* each element returned by the iterator in turn to see if it is contained in
* the specified collection {@code self}. If all elements are so contained,
* {@code true} is returned, otherwise {@code false}.
*
* @param self a collection which might contain all elements in {@code c}
* @param c a collection whose elements might be contained by {@code self}
*/
// TODO: Make public?
static boolean containsAll(Collection self, Collection c) {
checkNotNull(self);
for (Object o : c) {
if (!self.contains(o)) {
return false;
}
}
return true;
}
/**
* Converts an iterable into a collection. If the iterable is already a
* collection, it is returned. Otherwise, an {@link java.util.ArrayList} is
* created with the contents of the iterable in same iteration order.
*/
static Collection toCollection(Iterable iterable) {
return (iterable instanceof Collection)
? (Collection) iterable : Lists.newArrayList(iterable);
}
/**
* Returns the elements of {@code unfiltered} that satisfy a predicate. The
* returned collection is a live view of {@code unfiltered}; changes to one
* affect the other.
*
* The resulting collection's iterator does not support {@code remove()},
* but all other collection methods are supported. The collection's
* {@code add()} and {@code addAll()} methods throw an
* {@link IllegalArgumentException} if an element that doesn't satisfy the
* predicate is provided. When methods such as {@code removeAll()} and
* {@code clear()} are called on the filtered collection, only elements that
* satisfy the filter will be removed from the underlying collection.
*
*
The returned collection isn't threadsafe or serializable, even if
* {@code unfiltered} is.
*
*
Many of the filtered collection's methods, such as {@code size()},
* iterate across every element in the underlying collection and determine
* which elements satisfy the filter. When a live view is not needed,
* it may be faster to copy the filtered collection and use the copy.
*/
public static Collection filter(
Collection unfiltered, Predicate predicate) {
if (unfiltered instanceof FilteredCollection) {
// Support clear(), removeAll(), and retainAll() when filtering a filtered
// collection.
FilteredCollection filtered = (FilteredCollection) unfiltered;
Predicate combinedPredicate
= Predicates.and(filtered.predicate, predicate);
return new FilteredCollection(filtered.unfiltered, combinedPredicate);
}
return new FilteredCollection(
checkNotNull(unfiltered), checkNotNull(predicate));
}
static class FilteredCollection implements Collection {
final Collection unfiltered;
final Predicate predicate;
FilteredCollection(Collection unfiltered,
Predicate predicate) {
this.unfiltered = unfiltered;
this.predicate = predicate;
}
public boolean add(E element) {
checkArgument(predicate.apply(element));
return unfiltered.add(element);
}
public boolean addAll(Collection collection) {
for (E element : collection) {
checkArgument(predicate.apply(element));
}
return unfiltered.addAll(collection);
}
public void clear() {
Iterator iterator = unfiltered.iterator();
while (iterator.hasNext()) {
E element = iterator.next();
if (predicate.apply(element)) {
iterator.remove();
}
}
}
// if a ClassCastException occurs, contains() returns false
@SuppressWarnings("unchecked")
public boolean contains(Object element) {
try {
return predicate.apply((E) element) && unfiltered.contains(element);
} catch (NullPointerException e) {
return false;
} catch (ClassCastException e) {
return false;
}
}
public boolean containsAll(Collection collection) {
for (Object element : collection) {
if (!contains(element)) {
return false;
}
}
return true;
}
public boolean isEmpty() {
return !Iterators.any(unfiltered.iterator(), predicate);
}
public Iterator iterator() {
return Iterators.filter(unfiltered.iterator(), predicate);
}
// if a ClassCastException occurs, remove() returns false
@SuppressWarnings("unchecked")
public boolean remove(Object element) {
try {
return predicate.apply((E) element) && unfiltered.remove(element);
} catch (NullPointerException e) {
return false;
} catch (ClassCastException e) {
return false;
}
}
public boolean removeAll(Collection collection) {
checkNotNull(collection);
boolean changed = false;
Iterator iterator = unfiltered.iterator();
while (iterator.hasNext()) {
E element = iterator.next();
if (predicate.apply(element) && collection.contains(element)) {
iterator.remove();
changed = true;
}
}
return changed;
}
public boolean retainAll(Collection collection) {
checkNotNull(collection);
boolean changed = false;
Iterator iterator = unfiltered.iterator();
while (iterator.hasNext()) {
E element = iterator.next();
if (predicate.apply(element) && !collection.contains(element)) {
iterator.remove();
changed = true;
}
}
return changed;
}
public int size() {
return Iterators.size(iterator());
}
public Object[] toArray() {
// creating an ArrayList so filtering happens once
return Lists.newArrayList(iterator()).toArray();
}
public T[] toArray(T[] array) {
return Lists.newArrayList(iterator()).toArray(array);
}
@Override public String toString() {
return Iterators.toString(iterator());
}
}
/**
* Returns a collection that applies {@code function} to each element of
* {@code fromCollection}. The returned collection is a live view of {@code
* fromCollection}; changes to one affect the other.
*
* The returned collection's {@code add()} and {@code addAll()} methods
* throw an {@link UnsupportedOperationException}. All other collection
* methods are supported, as long as {@code fromCollection} supports them.
*
*
The returned collection isn't threadsafe or serializable, even if
* {@code fromCollection} is.
*
*
When a live view is not needed, it may be faster to copy the
* transformed collection and use the copy.
*/
static Collection transform(Collection fromCollection,
Function function) {
return new TransformedCollection(fromCollection, function);
}
static class TransformedCollection extends AbstractCollection {
final Collection fromCollection;
final Function function;
TransformedCollection(Collection fromCollection,
Function function) {
this.fromCollection = checkNotNull(fromCollection);
this.function = checkNotNull(function);
}
@Override public void clear() {
fromCollection.clear();
}
@Override public boolean isEmpty() {
return fromCollection.isEmpty();
}
@Override public Iterator iterator() {
return Iterators.transform(fromCollection.iterator(), function);
}
@Override public boolean removeAll(Collection c) {
return super.removeAll(checkNotNull(c));
}
@Override public boolean retainAll(Collection c) {
return super.retainAll(checkNotNull(c));
}
@Override public int size() {
return fromCollection.size();
}
}
static boolean setEquals(Set thisSet, @Nullable Object object) {
if (object == thisSet) {
return true;
}
if (object instanceof Set) {
Set thatSet = (Set) object;
return thisSet.size() == thatSet.size()
&& thisSet.containsAll(thatSet);
}
return false;
}
}