| /* |
| * Copyright (C) 2012 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 static com.google.common.base.Preconditions.checkArgument; |
| import static com.google.common.base.Preconditions.checkNotNull; |
| |
| import com.google.common.annotations.Beta; |
| import com.google.common.annotations.GwtCompatible; |
| import com.google.common.annotations.VisibleForTesting; |
| import com.google.errorprone.annotations.CanIgnoreReturnValue; |
| import java.io.Serializable; |
| import java.util.ArrayDeque; |
| import java.util.Collection; |
| import java.util.Queue; |
| |
| /** |
| * A non-blocking queue which automatically evicts elements from the head of the queue when |
| * attempting to add new elements onto the queue and it is full. This queue orders elements FIFO |
| * (first-in-first-out). This data structure is logically equivalent to a circular buffer (i.e., |
| * cyclic buffer or ring buffer). |
| * |
| * <p>An evicting queue must be configured with a maximum size. Each time an element is added to a |
| * full queue, the queue automatically removes its head element. This is different from conventional |
| * bounded queues, which either block or reject new elements when full. |
| * |
| * <p>This class is not thread-safe, and does not accept null elements. |
| * |
| * @author Kurt Alfred Kluever |
| * @since 15.0 |
| */ |
| @Beta |
| @GwtCompatible |
| public final class EvictingQueue<E> extends ForwardingQueue<E> implements Serializable { |
| |
| private final Queue<E> delegate; |
| |
| @VisibleForTesting final int maxSize; |
| |
| private EvictingQueue(int maxSize) { |
| checkArgument(maxSize >= 0, "maxSize (%s) must >= 0", maxSize); |
| this.delegate = new ArrayDeque<E>(maxSize); |
| this.maxSize = maxSize; |
| } |
| |
| /** |
| * Creates and returns a new evicting queue that will hold up to {@code maxSize} elements. |
| * |
| * <p>When {@code maxSize} is zero, elements will be evicted immediately after being added to the |
| * queue. |
| */ |
| public static <E> EvictingQueue<E> create(int maxSize) { |
| return new EvictingQueue<E>(maxSize); |
| } |
| |
| /** |
| * Returns the number of additional elements that this queue can accept without evicting; zero if |
| * the queue is currently full. |
| * |
| * @since 16.0 |
| */ |
| public int remainingCapacity() { |
| return maxSize - size(); |
| } |
| |
| @Override |
| protected Queue<E> delegate() { |
| return delegate; |
| } |
| |
| /** |
| * Adds the given element to this queue. If the queue is currently full, the element at the head |
| * of the queue is evicted to make room. |
| * |
| * @return {@code true} always |
| */ |
| @Override |
| @CanIgnoreReturnValue |
| public boolean offer(E e) { |
| return add(e); |
| } |
| |
| /** |
| * Adds the given element to this queue. If the queue is currently full, the element at the head |
| * of the queue is evicted to make room. |
| * |
| * @return {@code true} always |
| */ |
| @Override |
| @CanIgnoreReturnValue |
| public boolean add(E e) { |
| checkNotNull(e); // check before removing |
| if (maxSize == 0) { |
| return true; |
| } |
| if (size() == maxSize) { |
| delegate.remove(); |
| } |
| delegate.add(e); |
| return true; |
| } |
| |
| @Override |
| @CanIgnoreReturnValue |
| public boolean addAll(Collection<? extends E> collection) { |
| int size = collection.size(); |
| if (size >= maxSize) { |
| clear(); |
| return Iterables.addAll(this, Iterables.skip(collection, size - maxSize)); |
| } |
| return standardAddAll(collection); |
| } |
| |
| @Override |
| public boolean contains(Object object) { |
| return delegate().contains(checkNotNull(object)); |
| } |
| |
| @Override |
| @CanIgnoreReturnValue |
| public boolean remove(Object object) { |
| return delegate().remove(checkNotNull(object)); |
| } |
| |
| // TODO(kak): Do we want to checkNotNull each element in containsAll, removeAll, and retainAll? |
| |
| private static final long serialVersionUID = 0L; |
| } |