Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.io;
020
021import org.apache.reef.annotations.Unstable;
022
023import java.util.Map;
024import java.util.Set;
025
026/**
027 * A Map interface for data that can be swapped out to other processes, managed
028 * by native code, paged to disk, stored remotely, etc...
029 *
030 * @param <T> the entry type of the map
031 */
032@Unstable
033public interface ExternalMap<T> {
034
035  /**
036   * @param key
037   * @return true, if an entry with the given key exists
038   */
039  boolean containsKey(final CharSequence key);
040
041  /**
042   * Element access.
043   *
044   * @param key
045   * @return the object stored under key nor null if no such object exists
046   */
047  T get(final CharSequence key);
048
049  /**
050   * Put a record into the map.
051   *
052   * @param key
053   * @param value
054   * @return the previous value associated with key, or null if there was no
055   * mapping for key. (A null return can also indicate that the map previously
056   * associated null with key, if the implementation supports null values.)
057   */
058  T put(final CharSequence key, final T value);
059
060  /**
061   * Removes the mapping for a key from this map if it is present (optional
062   * operation). More formally, if this map contains a mapping from key k to
063   * value v such that (key==null ? k==null : key.equals(k)), that mapping is
064   * removed. (The map can contain at most one such mapping.) Returns the
065   * value to which this map previously associated the key, or null if the map
066   * contained no mapping for the key.
067   * <p>
068   * If this map permits null values, then a return value of null does not
069   * necessarily indicate that the map contained no mapping for the key; it's
070   * also possible that the map explicitly mapped the key to null.
071   * <p>
072   * The map will not contain a mapping for the specified key once the call
073   * returns.
074   *
075   * @param key key whose mapping is to be removed from the map
076   * @return the previous value associated with key, or null if there was no
077   * mapping for key.
078   */
079  T remove(final CharSequence key);
080
081  /**
082   * Copies all of the mappings from the specified map to this map (optional
083   * operation). The effect of this call is equivalent to that of calling
084   * put(k, v) on this map once for each mapping from key k to value v in the
085   * specified map. The behavior of this operation is undefined if the
086   * specified map is modified while the operation is in progress.
087   *
088   * @param m
089   */
090  void putAll(final Map<? extends CharSequence, ? extends T> m);
091
092  Iterable<Map.Entry<CharSequence, T>> getAll(Set<? extends CharSequence> keys);
093}