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/*
 * Copyright (c) 2008-2018, Hazelcast, Inc. All Rights Reserved.
 *
 * 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.hazelcast.jet.core;

import java.util.Collection;
import java.util.NoSuchElementException;
import java.util.function.Consumer;

/**
 * A subset of {@code Queue} API restricted to the consumer side,
 * with additional support for bulk draining operations.
 */
public interface Inbox {

    /**
     * Returns {@code true} if this inbox contains no elements, {@code false} otherwise.
     */
    boolean isEmpty();

    /**
     * Retrieves, but does not remove, the head of this inbox, or returns
     * {@code null} if it is empty.
     */
    Object peek();

    /**
     * Retrieves and removes the head of this inbox, or returns {@code null}
     * if it is empty.
     */
    Object poll();

    /**
     * Removes the head of this inbox. This method throws an exception
     * if the inbox is empty.
     *
     * @throws NoSuchElementException if this inbox is empty
     */
    void remove();

    /**
     * Drains all elements into the provided {@link Collection}.
     *
     * @param target the collection to drain this object's items into
     * @return the number of elements actually drained
     */
    default  int drainTo(Collection target) {
        int drained = 0;
        for (E o; (o = (E) poll()) != null; drained++) {
            target.add(o);
        }
        return drained;
    }

    /**
     * Passes each of this object's items to the supplied consumer until it is empty.
     *
     * @return the number of elements drained
     */
    default  int drain(Consumer consumer) {
        int consumed = 0;
        for (E o; (o = (E) poll()) != null; consumed++) {
            consumer.accept(o);
        }
        return consumed;
    }
}
 















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