Java tutorial
/* * Copyright (C) 2008 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 com.google.common.annotations.GwtCompatible; import com.google.common.base.Objects; import java.util.Collection; import java.util.Map; import java.util.Set; import javax.annotation.Nullable; /** * A collection that associates an ordered pair of keys, called a row key and a * column key, with a single value. A table may be sparse, with only a small * fraction of row key / column key pairs possessing a corresponding value. * * <p>The mappings corresponding to a given row key may be viewed as a {@link * Map} whose keys are the columns. The reverse is also available, associating a * column with a row key / value map. Note that, in some implementations, data * access by column key may have fewer supported operations or worse performance * than data access by row key. * * <p>The methods returning collections or maps always return views of the * underlying table. Updating the table can change the contents of those * collections, and updating the collections will change the table. * * <p>All methods that modify the table are optional, and the views returned by * the table may or may not be modifiable. When modification isn't supported, * those methods will throw an {@link UnsupportedOperationException}. * * <p>See the Guava User Guide article on <a href= * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#table"> * {@code Table}</a>. * * @author Jared Levy * @param <R> the type of the table row keys * @param <C> the type of the table column keys * @param <V> the type of the mapped values * @since 7.0 */ @GwtCompatible public interface Table<R, C, V> { // TODO(jlevy): Consider adding methods similar to ConcurrentMap methods. // Accessors /** * Returns {@code true} if the table contains a mapping with the specified * row and column keys. * * @param rowKey key of row to search for * @param columnKey key of column to search for */ boolean contains(@Nullable Object rowKey, @Nullable Object columnKey); /** * Returns {@code true} if the table contains a mapping with the specified * row key. * * @param rowKey key of row to search for */ boolean containsRow(@Nullable Object rowKey); /** * Returns {@code true} if the table contains a mapping with the specified * column. * * @param columnKey key of column to search for */ boolean containsColumn(@Nullable Object columnKey); /** * Returns {@code true} if the table contains a mapping with the specified * value. * * @param value value to search for */ boolean containsValue(@Nullable Object value); /** * Returns the value corresponding to the given row and column keys, or * {@code null} if no such mapping exists. * * @param rowKey key of row to search for * @param columnKey key of column to search for */ V get(@Nullable Object rowKey, @Nullable Object columnKey); /** Returns {@code true} if the table contains no mappings. */ boolean isEmpty(); /** * Returns the number of row key / column key / value mappings in the table. */ int size(); /** * Compares the specified object with this table for equality. Two tables are * equal when their cell views, as returned by {@link #cellSet}, are equal. */ @Override boolean equals(@Nullable Object obj); /** * Returns the hash code for this table. The hash code of a table is defined * as the hash code of its cell view, as returned by {@link #cellSet}. */ @Override int hashCode(); // Mutators /** Removes all mappings from the table. */ void clear(); /** * Associates the specified value with the specified keys. If the table * already contained a mapping for those keys, the old value is replaced with * the specified value. * * @param rowKey row key that the value should be associated with * @param columnKey column key that the value should be associated with * @param value value to be associated with the specified keys * @return the value previously associated with the keys, or {@code null} if * no mapping existed for the keys */ @Nullable V put(R rowKey, C columnKey, V value); /** * Copies all mappings from the specified table to this table. The effect is * equivalent to calling {@link #put} with each row key / column key / value * mapping in {@code table}. * * @param table the table to add to this table */ void putAll(Table<? extends R, ? extends C, ? extends V> table); /** * Removes the mapping, if any, associated with the given keys. * * @param rowKey row key of mapping to be removed * @param columnKey column key of mapping to be removed * @return the value previously associated with the keys, or {@code null} if * no such value existed */ @Nullable V remove(@Nullable Object rowKey, @Nullable Object columnKey); // Views /** * Returns a view of all mappings that have the given row key. For each row * key / column key / value mapping in the table with that row key, the * returned map associates the column key with the value. If no mappings in * the table have the provided row key, an empty map is returned. * * <p>Changes to the returned map will update the underlying table, and vice * versa. * * @param rowKey key of row to search for in the table * @return the corresponding map from column keys to values */ Map<C, V> row(R rowKey); /** * Returns a view of all mappings that have the given column key. For each row * key / column key / value mapping in the table with that column key, the * returned map associates the row key with the value. If no mappings in the * table have the provided column key, an empty map is returned. * * <p>Changes to the returned map will update the underlying table, and vice * versa. * * @param columnKey key of column to search for in the table * @return the corresponding map from row keys to values */ Map<R, V> column(C columnKey); /** * Returns a set of all row key / column key / value triplets. Changes to the * returned set will update the underlying table, and vice versa. The cell set * does not support the {@code add} or {@code addAll} methods. * * @return set of table cells consisting of row key / column key / value * triplets */ Set<Cell<R, C, V>> cellSet(); /** * Returns a set of row keys that have one or more values in the table. * Changes to the set will update the underlying table, and vice versa. * * @return set of row keys */ Set<R> rowKeySet(); /** * Returns a set of column keys that have one or more values in the table. * Changes to the set will update the underlying table, and vice versa. * * @return set of column keys */ Set<C> columnKeySet(); /** * Returns a collection of all values, which may contain duplicates. Changes * to the returned collection will update the underlying table, and vice * versa. * * @return collection of values */ Collection<V> values(); /** * Returns a view that associates each row key with the corresponding map from * column keys to values. Changes to the returned map will update this table. * The returned map does not support {@code put()} or {@code putAll()}, or * {@code setValue()} on its entries. * * <p>In contrast, the maps returned by {@code rowMap().get()} have the same * behavior as those returned by {@link #row}. Those maps may support {@code * setValue()}, {@code put()}, and {@code putAll()}. * * @return a map view from each row key to a secondary map from column keys to * values */ Map<R, Map<C, V>> rowMap(); /** * Returns a view that associates each column key with the corresponding map * from row keys to values. Changes to the returned map will update this * table. The returned map does not support {@code put()} or {@code putAll()}, * or {@code setValue()} on its entries. * * <p>In contrast, the maps returned by {@code columnMap().get()} have the * same behavior as those returned by {@link #column}. Those maps may support * {@code setValue()}, {@code put()}, and {@code putAll()}. * * @return a map view from each column key to a secondary map from row keys to * values */ Map<C, Map<R, V>> columnMap(); /** * Row key / column key / value triplet corresponding to a mapping in a table. * * @since 7.0 */ interface Cell<R, C, V> { /** * Returns the row key of this cell. */ @Nullable R getRowKey(); /** * Returns the column key of this cell. */ @Nullable C getColumnKey(); /** * Returns the value of this cell. */ @Nullable V getValue(); /** * Compares the specified object with this cell for equality. Two cells are * equal when they have equal row keys, column keys, and values. */ @Override boolean equals(@Nullable Object obj); /** * Returns the hash code of this cell. * * <p>The hash code of a table cell is equal to {@link * Objects#hashCode}{@code (e.getRowKey(), e.getColumnKey(), e.getValue())}. */ @Override int hashCode(); } }