139 lines
3.7 KiB
Java
139 lines
3.7 KiB
Java
/*
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* Copyright (C) 2012 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import static com.google.common.base.Preconditions.checkArgument;
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import static com.google.common.base.Preconditions.checkNotNull;
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import java.io.Serializable;
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import java.util.ArrayDeque;
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import java.util.Collection;
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import java.util.Queue;
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import com.google.common.annotations.Beta;
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import com.google.common.annotations.GwtIncompatible;
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import com.google.common.annotations.VisibleForTesting;
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/**
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* A non-blocking queue which automatically evicts elements from the head of the
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* queue when attempting to add new elements onto the queue and it is full.
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*
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* <p>
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* An evicting queue must be configured with a maximum size. Each time an
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* element is added to a full queue, the queue automatically removes its head
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* element. This is different from conventional bounded queues, which either
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* block or reject new elements when full.
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*
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* <p>
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* This class is not thread-safe, and does not accept null elements.
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*
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* @author Kurt Alfred Kluever
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* @since 15.0
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*/
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@Beta
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@GwtIncompatible("java.util.ArrayDeque")
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public final class EvictingQueue<E> extends ForwardingQueue<E> implements Serializable {
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private final Queue<E> delegate;
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@VisibleForTesting
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final int maxSize;
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private EvictingQueue(int maxSize) {
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checkArgument(maxSize >= 0, "maxSize (%s) must >= 0", maxSize);
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this.delegate = new ArrayDeque<E>(maxSize);
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this.maxSize = maxSize;
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}
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/**
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* Creates and returns a new evicting queue that will hold up to {@code maxSize}
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* elements.
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*
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* <p>
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* When {@code maxSize} is zero, elements will be evicted immediately after
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* being added to the queue.
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*/
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public static <E> EvictingQueue<E> create(int maxSize) {
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return new EvictingQueue<E>(maxSize);
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}
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/**
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* Returns the number of additional elements that this queue can accept without
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* evicting; zero if the queue is currently full.
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*
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* @since 16.0
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*/
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public int remainingCapacity() {
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return maxSize - size();
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}
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@Override
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protected Queue<E> delegate() {
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return delegate;
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}
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/**
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* Adds the given element to this queue. If the queue is currently full, the
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* element at the head of the queue is evicted to make room.
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*
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* @return {@code true} always
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*/
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@Override
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public boolean offer(E e) {
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return add(e);
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}
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/**
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* Adds the given element to this queue. If the queue is currently full, the
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* element at the head of the queue is evicted to make room.
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*
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* @return {@code true} always
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*/
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@Override
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public boolean add(E e) {
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checkNotNull(e); // check before removing
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if (maxSize == 0) {
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return true;
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}
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if (size() == maxSize) {
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delegate.remove();
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}
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delegate.add(e);
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return true;
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}
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@Override
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public boolean addAll(Collection<? extends E> collection) {
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return standardAddAll(collection);
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}
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@Override
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public boolean contains(Object object) {
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return delegate().contains(checkNotNull(object));
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}
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@Override
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public boolean remove(Object object) {
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return delegate().remove(checkNotNull(object));
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}
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// TODO(user): Do we want to checkNotNull each element in containsAll,
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// removeAll, and retainAll?
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private static final long serialVersionUID = 0L;
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}
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