com.google.common.collect
Class HashBasedTable<R,C,V>

java.lang.Object
  com.google.common.collect.HashBasedTable<R,C,V>

All Implemented Interfaces:

Table<R,C,V>, Serializable

@GwtCompatible(serializable=true)
@Beta
public class HashBasedTable<R,C,V>
extends Object

Implementation of Table using hash tables.

The views returned by column(C), columnKeySet(), and 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.

Since:

7

Author:

Jared Levy

See Also:

Serialized Form

create

public static <R,C,V> HashBasedTable<R,C,V> create()

Creates an empty HashBasedTable.

create

public static <R,C,V> HashBasedTable<R,C,V> create(int expectedRows,
                                                   int expectedCellsPerRow)

Creates an empty HashBasedTable with the specified map sizes.

Parameters:

expectedRows - the expected number of distinct row keys

expectedCellsPerRow - the expected number of column key / value mappings in each row

Throws:

IllegalArgumentException - if expectedRows or expectedCellsPerRow is negative

create

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

Creates a HashBasedTable with the same mappings as the specified table.

Parameters:

table - the table to copy

Throws:

NullPointerException - if any of the row keys, column keys, or values in table are null.

contains

public boolean contains(@Nullable
                        Object rowKey,
                        @Nullable
                        Object columnKey)

Description copied from interface: Table

Returns true if the table contains a mapping with the specified row and column keys.

Specified by:

contains in interface Table<R,C,V>

Parameters:

rowKey - key of row to search for

columnKey - key of column to search for

containsColumn

public boolean containsColumn(@Nullable
                              Object columnKey)

Description copied from interface: Table

Returns true if the table contains a mapping with the specified column.

Specified by:

containsColumn in interface Table<R,C,V>

Parameters:

columnKey - key of column to search for

containsRow

public boolean containsRow(@Nullable
                           Object rowKey)

Description copied from interface: Table

Returns true if the table contains a mapping with the specified row key.

Specified by:

containsRow in interface Table<R,C,V>

Parameters:

rowKey - key of row to search for

containsValue

public boolean containsValue(@Nullable
                             Object value)

Description copied from interface: Table

Returns true if the table contains a mapping with the specified value.

Specified by:

containsValue in interface Table<R,C,V>

Parameters:

value - value to search for

get

public V get(@Nullable
             Object rowKey,
             @Nullable
             Object columnKey)

Description copied from interface: Table

Returns the value corresponding to the given row and column keys, or null if no such mapping exists.

Specified by:

get in interface Table<R,C,V>

Parameters:

rowKey - key of row to search for

columnKey - key of column to search for

equals

public boolean equals(@Nullable
                      Object obj)

Description copied from class: java.lang.Object

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
• For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Specified by:

equals in interface Table<R,C,V>

Parameters:

obj - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), Hashtable

remove

public V remove(@Nullable
                Object rowKey,
                @Nullable
                Object columnKey)

Description copied from interface: Table

Removes the mapping, if any, associated with the given keys.

Specified by:

remove in interface Table<R,C,V>

Parameters:

rowKey - row key of mapping to be removed

columnKey - column key of mapping to be removed

Returns:

the value previously associated with the keys, or null if no such value existed

isEmpty

public boolean isEmpty()

Description copied from interface: Table

Returns true if the table contains no mappings.

Specified by:

isEmpty in interface Table<R,C,V>

size

public int size()

Description copied from interface: Table

Returns the number of row key / column key / value mappings in the table.

Specified by:

size in interface Table<R,C,V>

hashCode

public int hashCode()

Description copied from class: java.lang.Object

Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

• Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
• If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
• It is not required that if two objects are unequal according to the Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java^TM programming language.)

Specified by:

hashCode in interface Table<R,C,V>

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), Hashtable

toString

public String toString()

Returns the string representation rowMap().toString().

Overrides:

toString in class Object

Returns:

a string representation of the object.

clear

public void clear()

Description copied from interface: Table

Removes all mappings from the table.

Specified by:

clear in interface Table<R,C,V>

put

public V put(R rowKey,
             C columnKey,
             V value)

Description copied from interface: Table

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.

Specified by:

put in interface Table<R,C,V>

Parameters:

rowKey - row key that the value should be associated with

columnKey - column key that the value should be associated with

value - value to be associated with the specified keys

Returns:

the value previously associated with the keys, or null if no mapping existed for the keys

putAll

public void putAll(Table<? extends R,? extends C,? extends V> table)

Description copied from interface: Table

Copies all mappings from the specified table to this table. The effect is equivalent to calling Table.put(R, C, V) with each row key / column key / value mapping in table.

Specified by:

putAll in interface Table<R,C,V>

Parameters:

table - the table to add to this table

cellSet

public Set<Table.Cell<R,C,V>> cellSet()

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 add or addAll methods.

The set's iterator traverses the mappings for the first row, the mappings for the second row, and so on.

Each cell is an immutable snapshot of a row key / column key / value mapping, taken at the time the cell is returned by a method call to the set or its iterator.

Specified by:

cellSet in interface Table<R,C,V>

Returns:

set of table cells consisting of row key / column key / value triplets

row

public Map<C,V> row(R rowKey)

Description copied from interface: Table

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.

Changes to the returned map will update the underlying table, and vice versa.

Specified by:

row in interface Table<R,C,V>

Parameters:

rowKey - key of row to search for in the table

Returns:

the corresponding map from column keys to values

column

public Map<R,V> column(C columnKey)

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.

Changes to the returned map will update the underlying table, and vice versa.

The returned map's views have iterators that don't support remove().

Specified by:

column in interface Table<R,C,V>

Parameters:

columnKey - key of column to search for in the table

Returns:

the corresponding map from row keys to values

rowKeySet

public Set<R> rowKeySet()

Description copied from interface: Table

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.

Specified by:

rowKeySet in interface Table<R,C,V>

Returns:

set of row keys

columnKeySet

public Set<C> columnKeySet()

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.

The returned set has an iterator that does not support remove().

The set's iterator traverses the columns of the first row, the columns of the second row, etc., skipping any columns that have appeared previously.

Specified by:

columnKeySet in interface Table<R,C,V>

Returns:

set of column keys

values

public Collection<V> values()

Returns a collection of all values, which may contain duplicates. Changes to the returned collection will update the underlying table, and vice versa.

The collection's iterator traverses the values for the first row, the values for the second row, and so on.

Specified by:

values in interface Table<R,C,V>

Returns:

collection of values

rowMap

public Map<R,Map<C,V>> rowMap()

Description copied from interface: Table

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 put() or putAll(), or setValue() on its entries.

In contrast, the maps returned by rowMap().get() have the same behavior as those returned by Table.row(R). Those maps may support setValue(), put(), and putAll().

Specified by:

rowMap in interface Table<R,C,V>

Returns:

a map view from each row key to a secondary map from column keys to values

columnMap

public Map<C,Map<R,V>> columnMap()

Description copied from interface: Table

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 put() or putAll(), or setValue() on its entries.

In contrast, the maps returned by columnMap().get() have the same behavior as those returned by Table.column(C). Those maps may support setValue(), put(), and putAll().

Specified by:

columnMap in interface Table<R,C,V>

Returns:

a map view from each column key to a secondary map from row keys to values