java.util
Class Collections.UnmodifiableMap

java.lang.Object
  java.util.Collections.UnmodifiableMap

All Implemented Interfaces:

Map, Serializable

Direct Known Subclasses:

Collections.UnmodifiableSortedMap

Enclosing class:

Collections

private static class Collections.UnmodifiableMap

extends Object

implements Map, Serializable

See Also:

Serialized Form

Nested Class Summary

(package private) static class

Collections.UnmodifiableMap.UnmodifiableEntrySet We need this class in addition to UnmodifiableSet as Map.Entries themselves permit modification of the backing Map via their setValue operation.

Nested classes inherited from class java.util.Map

Map.Entry

Field Summary

private Set	entrySet
private Set	keySet
private Map	m
private static long	serialVersionUID
private Collection	values

Constructor Summary

(package private)

Collections.UnmodifiableMap(Map m)

Method Summary

void	clear() Removes all mappings from this map (optional operation).
boolean	containsKey(Object key) Returns true if this map contains a mapping for the specified key.
boolean	containsValue(Object val) Returns true if this map maps one or more keys to the specified value.
Set	entrySet() Returns a set view of the mappings contained in this map.
boolean	equals(Object o) Compares the specified object with this map for equality.
Object	get(Object key) Returns the value to which this map maps the specified key.
int	hashCode() Returns the hash code value for this map.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
Set	keySet() Returns a set view of the keys contained in this map.
Object	put(Object key, Object value) Associates the specified value with the specified key in this map (optional operation).
void	putAll(Map t) Copies all of the mappings from the specified map to this map (optional operation).
Object	remove(Object key) Removes the mapping for this key from this map if it is present (optional operation).
int	size() Returns the number of key-value mappings in this map.
String	toString() Returns a string representation of the object.
Collection	values() Returns a collection view of the values contained in this map.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

m

private final Map m

keySet

private transient Set keySet

entrySet

private transient Set entrySet

values

private transient Collection values

Constructor Detail

Collections.UnmodifiableMap

Collections.UnmodifiableMap(Map m)

Method Detail

size

public int size()

Description copied from interface: Map

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface Map

Returns:

the number of key-value mappings in this map.

isEmpty

public boolean isEmpty()

Description copied from interface: Map

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

Specified by:

isEmpty in interface Map

Returns:

true if this map contains no key-value mappings.

containsKey

public boolean containsKey(Object key)

Description copied from interface: Map

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains at 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

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 boolean containsValue(Object val)

Description copied from interface: 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

Parameters:

val - 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 Object get(Object key)

Description copied from interface: Map

Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. 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.

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.)

Specified by:

get in interface Map

Parameters:

key - key whose associated value is to be returned.

Returns:

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

See Also:

Map.containsKey(Object)

put

public Object put(Object key,
                  Object value)

Description copied from interface: Map

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))

Specified by:

put in interface Map

Parameters:

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

value - value to be associated with the specified key.

Returns:

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

remove

public Object remove(Object key)

Description copied from interface: Map

Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

Specified by:

remove in interface Map

Parameters:

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

Returns:

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

putAll

public void putAll(Map t)

Description copied from interface: Map

Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.

Specified by:

putAll in interface Map

Parameters:

t - Mappings to be stored in this map.

clear

public void clear()

Description copied from interface: Map

Removes all mappings from this map (optional operation).

Specified by:

clear in interface Map

keySet

public Set keySet()

Description copied from interface: Map

Returns a set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

keySet in interface Map

Returns:

a set view of the keys contained in this map.

entrySet

public Set entrySet()

Description copied from interface: Map

Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

entrySet in interface Map

Returns:

a set view of the mappings contained in this map.

values

public Collection values()

Description copied from interface: Map

Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface Map

Returns:

a collection view of the values contained in this map.

equals

public boolean equals(Object o)

Description copied from interface: Map

Compares the specified object with this map for equality. Returns true if the given object is also a map and the two Maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.entrySet().equals(t2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

Specified by:

equals in interface Map

Overrides:

equals in class Object

Parameters:

o - 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 interface: Map

Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hashCodes of each entry in the map's entrySet view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.

Specified by:

hashCode in interface Map

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: 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.