com.google.common.collect

Class Tables

java.lang.Object

com.google.common.collect.Tables

@GwtCompatible
public final class Tables
extends Object

Provides static methods that involve a Table.

See the Guava User Guide article on Tables.

Since:

7.0

Author:

Jared Levy, Louis Wasserman

Method Summary

Modifier and Type	Method and Description
static <R,C,V> Table.Cell<R,C,V>	immutableCell(R rowKey, C columnKey, V value) Returns an immutable cell with the specified row key, column key, and value.
static <R,C,V> Table<R,C,V>	newCustomTable(Map<R,Map<C,V>> backingMap, Supplier<? extends Map<C,V>> factory) Creates a table that uses the specified backing map and factory.
static <R,C,V> Table<R,C,V>	synchronizedTable(Table<R,C,V> table) Returns a synchronized (thread-safe) table backed by the specified table.
static <T,R,C,V,I extends Table<R,C,V>> Collector<T,?,I>	toTable(Function<? super T,? extends R> rowFunction, Function<? super T,? extends C> columnFunction, Function<? super T,? extends V> valueFunction, BinaryOperator<V> mergeFunction, Supplier<I> tableSupplier) Returns a Collector that accumulates elements into a Table created using the specified supplier, whose cells are generated by applying the provided mapping functions to the input elements.
static <T,R,C,V,I extends Table<R,C,V>> Collector<T,?,I>	toTable(Function<? super T,? extends R> rowFunction, Function<? super T,? extends C> columnFunction, Function<? super T,? extends V> valueFunction, Supplier<I> tableSupplier) Returns a Collector that accumulates elements into a Table created using the specified supplier, whose cells are generated by applying the provided mapping functions to the input elements.
static <R,C,V1,V2> Table<R,C,V2>	transformValues(Table<R,C,V1> fromTable, Function<? super V1,V2> function) Returns a view of a table where each value is transformed by a function.
static <R,C,V> Table<C,R,V>	transpose(Table<R,C,V> table) Creates a transposed view of a given table that flips its row and column keys.
static <R,C,V> RowSortedTable<R,C,V>	unmodifiableRowSortedTable(RowSortedTable<R,? extends C,? extends V> table) Returns an unmodifiable view of the specified row-sorted table.
static <R,C,V> Table<R,C,V>	unmodifiableTable(Table<? extends R,? extends C,? extends V> table) Returns an unmodifiable view of the specified table.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

toTable

@Beta
public static <T,R,C,V,I extends Table<R,C,V>> Collector<T,?,I> toTable(Function<? super T,? extends R> rowFunction,
                                                                              Function<? super T,? extends C> columnFunction,
                                                                              Function<? super T,? extends V> valueFunction,
                                                                              Supplier<I> tableSupplier)

Returns a Collector that accumulates elements into a Table created using the specified supplier, whose cells are generated by applying the provided mapping functions to the input elements. Cells are inserted into the generated Table in encounter order.

If multiple input elements map to the same row and column, an IllegalStateException is thrown when the collection operation is performed.

Since:

21.0

toTable

public static <T,R,C,V,I extends Table<R,C,V>> Collector<T,?,I> toTable(Function<? super T,? extends R> rowFunction,
                                                                        Function<? super T,? extends C> columnFunction,
                                                                        Function<? super T,? extends V> valueFunction,
                                                                        BinaryOperator<V> mergeFunction,
                                                                        Supplier<I> tableSupplier)

Returns a Collector that accumulates elements into a Table created using the specified supplier, whose cells are generated by applying the provided mapping functions to the input elements. Cells are inserted into the generated Table in encounter order.

If multiple input elements map to the same row and column, the specified merging function is used to combine the values. Like Collectors.toMap(java.util.function.Function, java.util.function.Function, BinaryOperator, java.util.function.Supplier), this Collector throws a NullPointerException on null values returned from valueFunction, and treats nulls returned from mergeFunction as removals of that row/column pair.

Since:

21.0

immutableCell

public static <R,C,V> Table.Cell<R,C,V> immutableCell(@NullableDecl
                                                      R rowKey,
                                                      @NullableDecl
                                                      C columnKey,
                                                      @NullableDecl
                                                      V value)

Returns an immutable cell with the specified row key, column key, and value.

The returned cell is serializable.

Parameters:

rowKey - the row key to be associated with the returned cell

columnKey - the column key to be associated with the returned cell

value - the value to be associated with the returned cell

transpose

public static <R,C,V> Table<C,R,V> transpose(Table<R,C,V> table)

Creates a transposed view of a given table that flips its row and column keys. In other words, calling get(columnKey, rowKey) on the generated table always returns the same value as calling get(rowKey, columnKey) on the original table. Updating the original table changes the contents of the transposed table and vice versa.

The returned table supports update operations as long as the input table supports the analogous operation with swapped rows and columns. For example, in a HashBasedTable instance, rowKeySet().iterator() supports remove() but columnKeySet().iterator() doesn't. With a transposed HashBasedTable, it's the other way around.

newCustomTable

@Beta
public static <R,C,V> Table<R,C,V> newCustomTable(Map<R,Map<C,V>> backingMap,
                                                        Supplier<? extends Map<C,V>> factory)

Creates a table that uses the specified backing map and factory. It can generate a table based on arbitrary Map classes.

The factory-generated and backingMap classes determine the table iteration order. However, the table's row() method returns instances of a different class than factory.get() does.

Call this method only when the simpler factory methods in classes like HashBasedTable and TreeBasedTable won't suffice.

The views returned by the Table methods Table.column(C), Table.columnKeySet(), and Table.columnMap() have iterators that don't support remove(). Otherwise, all optional operations are supported. Null row keys, columns keys, and values are not supported.

Lookups by row key are often faster than lookups by column key, because the data is stored in a Map<R, Map<C, V>>. A method call like column(columnKey).get(rowKey) still runs quickly, since the row key is provided. However, column(columnKey).size() takes longer, since an iteration across all row keys occurs.

Note that this implementation is not synchronized. If multiple threads access this table concurrently and one of the threads modifies the table, it must be synchronized externally.

The table is serializable if backingMap, factory, the maps generated by factory, and the table contents are all serializable.

Note: the table assumes complete ownership over of backingMap and the maps returned by factory. Those objects should not be manually updated and they should not use soft, weak, or phantom references.

Parameters:

backingMap - place to store the mapping from each row key to its corresponding column key / value map

factory - supplier of new, empty maps that will each hold all column key / value mappings for a given row key

Throws:

IllegalArgumentException - if backingMap is not empty

Since:

10.0

transformValues

@Beta
public static <R,C,V1,V2> Table<R,C,V2> transformValues(Table<R,C,V1> fromTable,
                                                              Function<? super V1,V2> function)

Returns a view of a table where each value is transformed by a function. All other properties of the table, such as iteration order, are left intact.

Changes in the underlying table are reflected in this view. Conversely, this view supports removal operations, and these are reflected in the underlying table.

It's acceptable for the underlying table to contain null keys, and even null values provided that the function is capable of accepting null input. The transformed table might contain null values, if the function sometimes gives a null result.

The returned table is not thread-safe or serializable, even if the underlying table is.

The function is applied lazily, invoked when needed. This is necessary for the returned table to be a view, but it means that the function will be applied many times for bulk operations like Table.containsValue(java.lang.Object) and Table.toString(). For this to perform well, function should be fast. To avoid lazy evaluation when the returned table doesn't need to be a view, copy the returned table into a new table of your choosing.

Since:

10.0

unmodifiableTable

public static <R,C,V> Table<R,C,V> unmodifiableTable(Table<? extends R,? extends C,? extends V> table)

Returns an unmodifiable view of the specified table. This method allows modules to provide users with "read-only" access to internal tables. Query operations on the returned table "read through" to the specified table, and attempts to modify the returned table, whether direct or via its collection views, result in an UnsupportedOperationException.

The returned table will be serializable if the specified table is serializable.

Consider using an ImmutableTable, which is guaranteed never to change.

Since:

11.0

unmodifiableRowSortedTable

@Beta
public static <R,C,V> RowSortedTable<R,C,V> unmodifiableRowSortedTable(RowSortedTable<R,? extends C,? extends V> table)

Returns an unmodifiable view of the specified row-sorted table. This method allows modules to provide users with "read-only" access to internal tables. Query operations on the returned table "read through" to the specified table, and attempts to modify the returned table, whether direct or via its collection views, result in an UnsupportedOperationException.

The returned table will be serializable if the specified table is serializable.

Parameters:

table - the row-sorted table for which an unmodifiable view is to be returned

Returns:

an unmodifiable view of the specified table

Since:

11.0

synchronizedTable

public static <R,C,V> Table<R,C,V> synchronizedTable(Table<R,C,V> table)

Returns a synchronized (thread-safe) table backed by the specified table. In order to guarantee serial access, it is critical that all access to the backing table is accomplished through the returned table.

It is imperative that the user manually synchronize on the returned table when accessing any of its collection views:

 Table<R, C, V> table = Tables.synchronizedTable(HashBasedTable.<R, C, V>create());
 ...
 Map<C, V> row = table.row(rowKey);  // Needn't be in synchronized block
 ...
 synchronized (table) {  // Synchronizing on table, not row!
   Iterator<Entry<C, V>> i = row.entrySet().iterator(); // Must be in synchronized block
   while (i.hasNext()) {
     foo(i.next());
   }
 }
 

Failure to follow this advice may result in non-deterministic behavior.

The returned table will be serializable if the specified table is serializable.

Parameters:

table - the table to be wrapped in a synchronized view

Returns:

a synchronized view of the specified table

Since:

22.0