com.google.common.collect.ForwardingCollection Maven / Gradle / Ivy
/*
* Copyright (C) 2007 The Guava Authors
*
* 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.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Iterator;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A collection which forwards all its method calls to another collection. Subclasses should
* override one or more methods to modify the behavior of the backing collection as desired per the
* decorator pattern.
*
* Warning: The methods of {@code ForwardingCollection} forward indiscriminately to
* the methods of the delegate. For example, overriding {@link #add} alone will not change
* the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
* override {@code addAll} as well, either providing your own implementation, or delegating to the
* provided {@code standardAddAll} method.
*
*
{@code default} method warning: This class does not forward calls to {@code
* default} methods. Instead, it inherits their default implementations. When those implementations
* invoke methods, they invoke methods on the {@code ForwardingCollection}.
*
*
The {@code standard} methods are not guaranteed to be thread-safe, even when all of the
* methods that they depend on are thread-safe.
*
* @author Kevin Bourrillion
* @author Louis Wasserman
* @since 2.0
*/
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingCollection extends ForwardingObject
implements Collection {
// TODO(lowasser): identify places where thread safety is actually lost
/** Constructor for use by subclasses. */
protected ForwardingCollection() {}
@Override
protected abstract Collection delegate();
@Override
public Iterator iterator() {
return delegate().iterator();
}
@Override
public int size() {
return delegate().size();
}
@CanIgnoreReturnValue
@Override
public boolean removeAll(Collection collection) {
return delegate().removeAll(collection);
}
@Override
public boolean isEmpty() {
return delegate().isEmpty();
}
@Override
public boolean contains(@CheckForNull Object object) {
return delegate().contains(object);
}
@CanIgnoreReturnValue
@Override
public boolean add(@ParametricNullness E element) {
return delegate().add(element);
}
@CanIgnoreReturnValue
@Override
public boolean remove(@CheckForNull Object object) {
return delegate().remove(object);
}
@Override
public boolean containsAll(Collection collection) {
return delegate().containsAll(collection);
}
@CanIgnoreReturnValue
@Override
public boolean addAll(Collection collection) {
return delegate().addAll(collection);
}
@CanIgnoreReturnValue
@Override
public boolean retainAll(Collection collection) {
return delegate().retainAll(collection);
}
@Override
public void clear() {
delegate().clear();
}
@Override
public Object[] toArray() {
return delegate().toArray();
}
@CanIgnoreReturnValue
@Override
@SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
public T[] toArray(T[] array) {
return delegate().toArray(array);
}
/**
* A sensible definition of {@link #contains} in terms of {@link #iterator}. If you override
* {@link #iterator}, you may wish to override {@link #contains} to forward to this
* implementation.
*
* @since 7.0
*/
protected boolean standardContains(@CheckForNull Object object) {
return Iterators.contains(iterator(), object);
}
/**
* A sensible definition of {@link #containsAll} in terms of {@link #contains} . If you override
* {@link #contains}, you may wish to override {@link #containsAll} to forward to this
* implementation.
*
* @since 7.0
*/
protected boolean standardContainsAll(Collection collection) {
return Collections2.containsAllImpl(this, collection);
}
/**
* A sensible definition of {@link #addAll} in terms of {@link #add}. If you override {@link
* #add}, you may wish to override {@link #addAll} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardAddAll(Collection collection) {
return Iterators.addAll(this, collection.iterator());
}
/**
* A sensible definition of {@link #remove} in terms of {@link #iterator}, using the iterator's
* {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
* #remove} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardRemove(@CheckForNull Object object) {
Iterator iterator = iterator();
while (iterator.hasNext()) {
if (Objects.equal(iterator.next(), object)) {
iterator.remove();
return true;
}
}
return false;
}
/**
* A sensible definition of {@link #removeAll} in terms of {@link #iterator}, using the iterator's
* {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
* #removeAll} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardRemoveAll(Collection collection) {
return Iterators.removeAll(iterator(), collection);
}
/**
* A sensible definition of {@link #retainAll} in terms of {@link #iterator}, using the iterator's
* {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
* #retainAll} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardRetainAll(Collection collection) {
return Iterators.retainAll(iterator(), collection);
}
/**
* A sensible definition of {@link #clear} in terms of {@link #iterator}, using the iterator's
* {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
* #clear} to forward to this implementation.
*
* @since 7.0
*/
protected void standardClear() {
Iterators.clear(iterator());
}
/**
* A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}. If you override
* {@link #isEmpty}, you may wish to override {@link #isEmpty} to forward to this implementation.
* Alternately, it may be more efficient to implement {@code isEmpty} as {@code size() == 0}.
*
* @since 7.0
*/
protected boolean standardIsEmpty() {
return !iterator().hasNext();
}
/**
* A sensible definition of {@link #toString} in terms of {@link #iterator}. If you override
* {@link #iterator}, you may wish to override {@link #toString} to forward to this
* implementation.
*
* @since 7.0
*/
protected String standardToString() {
return Collections2.toStringImpl(this);
}
/**
* A sensible definition of {@link #toArray()} in terms of {@link #toArray(Object[])}. If you
* override {@link #toArray(Object[])}, you may wish to override {@link #toArray} to forward to
* this implementation.
*
* @since 7.0
*/
protected Object[] standardToArray() {
Object[] newArray = new Object[size()];
return toArray(newArray);
}
/**
* A sensible definition of {@link #toArray(Object[])} in terms of {@link #size} and {@link
* #iterator}. If you override either of these methods, you may wish to override {@link #toArray}
* to forward to this implementation.
*
* @since 7.0
*/
protected T[] standardToArray(T[] array) {
return ObjectArrays.toArrayImpl(this, array);
}
}