eaglercraft-1.8/sources/main/java/com/google/common/collect/EvictingQueue.java

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2022-12-25 01:12:28 -08:00
/*
* 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 java.io.Serializable;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Queue;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
/**
* 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.
*
* <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
@GwtIncompatible("java.util.ArrayDeque")
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
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
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
public boolean addAll(Collection<? extends E> collection) {
return standardAddAll(collection);
}
@Override
public boolean contains(Object object) {
return delegate().contains(checkNotNull(object));
}
@Override
public boolean remove(Object object) {
return delegate().remove(checkNotNull(object));
}
// TODO(user): Do we want to checkNotNull each element in containsAll,
// removeAll, and retainAll?
private static final long serialVersionUID = 0L;
}