com.google.common.collect
Class ImmutableMap<K,V>

java.lang.Object
  com.google.common.collect.ImmutableMap<K,V>

All Implemented Interfaces:

Serializable, Map<K,V>

Direct Known Subclasses:

ImmutableBiMap, ImmutableSortedMap

@GwtCompatible(serializable=true,
               emulated=true)
public abstract class ImmutableMap<K,V>
extends Object
implements Map<K,V>, Serializable

An immutable, hash-based Map with reliable user-specified iteration order. Does not permit null keys or values.

Unlike Collections.unmodifiableMap(java.util.Map), which is a view of a separate map which can still change, an instance of ImmutableMap contains its own data and will never change. ImmutableMap is convenient for public static final maps ("constant maps") and also lets you easily make a "defensive copy" of a map provided to your class by a caller.

Performance notes: unlike HashMap, ImmutableMap is not optimized for element types that have slow Object.equals(java.lang.Object) or Object.hashCode() implementations. You can get better performance by having your element type cache its own hash codes, and by making use of the cached values to short-circuit a slow equals algorithm.

Since:

2 (imported from Google Collections Library)

Author:

Jesse Wilson, Kevin Bourrillion

See Also:

Serialized Form

of

public static <K,V> ImmutableMap<K,V> of()

Returns the empty map. This map behaves and performs comparably to Collections.emptyMap(), and is preferable mainly for consistency and maintainability of your code.

of

public static <K,V> ImmutableMap<K,V> of(K k1,
                                         V v1)

Returns an immutable map containing a single entry. This map behaves and performs comparably to Collections.singletonMap(K, V) but will not accept a null key or value. It is preferable mainly for consistency and maintainability of your code.

of

public static <K,V> ImmutableMap<K,V> of(K k1,
                                         V v1,
                                         K k2,
                                         V v2)

Returns an immutable map containing the given entries, in order.

Throws:

IllegalArgumentException - if duplicate keys are provided

of

public static <K,V> ImmutableMap<K,V> of(K k1,
                                         V v1,
                                         K k2,
                                         V v2,
                                         K k3,
                                         V v3)

Returns an immutable map containing the given entries, in order.

Throws:

IllegalArgumentException - if duplicate keys are provided

of

public static <K,V> ImmutableMap<K,V> of(K k1,
                                         V v1,
                                         K k2,
                                         V v2,
                                         K k3,
                                         V v3,
                                         K k4,
                                         V v4)

Returns an immutable map containing the given entries, in order.

Throws:

IllegalArgumentException - if duplicate keys are provided

of

public static <K,V> ImmutableMap<K,V> of(K k1,
                                         V v1,
                                         K k2,
                                         V v2,
                                         K k3,
                                         V v3,
                                         K k4,
                                         V v4,
                                         K k5,
                                         V v5)

Returns an immutable map containing the given entries, in order.

Throws:

IllegalArgumentException - if duplicate keys are provided

builder

public static <K,V> ImmutableMap.Builder<K,V> builder()

Returns a new builder. The generated builder is equivalent to the builder created by the ImmutableMap.Builder constructor.

copyOf

public static <K,V> ImmutableMap<K,V> copyOf(Map<? extends K,? extends V> map)

Returns an immutable map containing the same entries as map. If map somehow contains entries with duplicate keys (for example, if it is a SortedMap whose comparator is not consistent with equals), the results of this method are undefined.

Despite the method name, this method attempts to avoid actually copying the data when it is safe to do so. The exact circumstances under which a copy will or will not be performed are undocumented and subject to change.

Throws:

NullPointerException - if any key or value in map is null

put

public final V put(K k,
                   V v)

Guaranteed to throw an exception and leave the map unmodified.

Specified by:

put in interface Map<K,V>

Parameters:

k - key with which the specified value is to be associated

v - value to be associated with the specified key

Returns:

the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)

Throws:

UnsupportedOperationException - always

remove

public final V remove(Object o)

Guaranteed to throw an exception and leave the map unmodified.

Specified by:

remove in interface Map<K,V>

Parameters:

o - key whose mapping is to be removed from the map

Returns:

the previous value associated with key, or null if there was no mapping for key.

Throws:

UnsupportedOperationException - always

putAll

public final void putAll(Map<? extends K,? extends V> map)

Guaranteed to throw an exception and leave the map unmodified.

Specified by:

putAll in interface Map<K,V>

Parameters:

map - mappings to be stored in this map

Throws:

UnsupportedOperationException - always

clear

public final void clear()

Guaranteed to throw an exception and leave the map unmodified.

Specified by:

clear in interface Map<K,V>

Throws:

UnsupportedOperationException - always

isEmpty

public boolean isEmpty()

Description copied from interface: java.util.Map

Returns true if this map contains no key-value mappings.

Specified by:

isEmpty in interface Map<K,V>

Returns:

true if this map contains no key-value mappings

containsKey

public boolean containsKey(@Nullable
                           Object key)

Description copied from interface: java.util.Map

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Specified by:

containsKey in interface Map<K,V>

Parameters:

key - key whose presence in this map is to be tested

Returns:

true if this map contains a mapping for the specified key

containsValue

public abstract boolean containsValue(@Nullable
                                      Object value)

Description copied from interface: java.util.Map

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

Specified by:

containsValue in interface Map<K,V>

Parameters:

value - value whose presence in this map is to be tested

Returns:

true if this map maps one or more keys to the specified value

get

public abstract V get(@Nullable
                      Object key)

Description copied from interface: java.util.Map

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

If this map permits null values, then a return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Specified by:

get in interface Map<K,V>

Parameters:

key - the key whose associated value is to be returned

Returns:

the value to which the specified key is mapped, or null if this map contains no mapping for the key

entrySet

public abstract ImmutableSet<Map.Entry<K,V>> entrySet()

Returns an immutable set of the mappings in this map. The entries are in the same order as the parameters used to build this map.

Specified by:

entrySet in interface Map<K,V>

Returns:

a set view of the mappings contained in this map

keySet

public abstract ImmutableSet<K> keySet()

Returns an immutable set of the keys in this map. These keys are in the same order as the parameters used to build this map.

Specified by:

keySet in interface Map<K,V>

Returns:

a set view of the keys contained in this map

values

public abstract ImmutableCollection<V> values()

Returns an immutable collection of the values in this map. The values are in the same order as the parameters used to build this map.

Specified by:

values in interface Map<K,V>

Returns:

a collection view of the values contained in this map

equals

public boolean equals(@Nullable
                      Object object)

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 Map<K,V>

Overrides:

equals in class Object

Parameters:

object - 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

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 Map<K,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()

Description copied from class: java.lang.Object

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Overrides:

toString in class Object

Returns:

a string representation of the object.