java.util.Map Maven / Gradle / Ivy
/*
This is not an official specification document, and usage is restricted.
NOTICE
(c) 2005-2007 Sun Microsystems, Inc. All Rights Reserved.
Neither this file nor any files generated from it describe a complete
specification, and they may only be used as described below. For
example, no permission is given for you to incorporate this file, in
whole or in part, in an implementation of a Java specification.
Sun Microsystems Inc. owns the copyright in this file and it is provided
to you for informative, as opposed to normative, use. The file and any
files generated from it may be used to generate other informative
documentation, such as a unified set of documents of API signatures for
a platform that includes technologies expressed as Java APIs. The file
may also be used to produce "compilation stubs," which allow
applications to be compiled and validated for such platforms.
Any work generated from this file, such as unified javadocs or compiled
stub files, must be accompanied by this notice in its entirety.
This work corresponds to the API signatures of JSR 219: Foundation
Profile 1.1. In the event of a discrepency between this work and the
JSR 219 specification, which is available at
http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence.
*/
package java.util;
/**
* An object that maps keys to values. A map cannot contain duplicate keys;
* each key can map to at most one value.
*
*
This interface takes the place of the Dictionary class, which
* was a totally abstract class rather than an interface.
*
*
The Map interface provides three collection views, which
* allow a map's contents to be viewed as a set of keys, collection of values,
* or set of key-value mappings. The order of a map is defined as
* the order in which the iterators on the map's collection views return their
* elements. Some map implementations, like the TreeMap class, make
* specific guarantees as to their order; others, like the HashMap
* class, do not.
*
*
Note: great care must be exercised if mutable objects are used as map
* keys. The behavior of a map is not specified if the value of an object is
* changed in a manner that affects equals comparisons while the object is a
* key in the map. A special case of this prohibition is that it is not
* permissible for a map to contain itself as a key. While it is permissible
* for a map to contain itself as a value, extreme caution is advised: the
* equals and hashCode methods are no longer well defined on a such a map.
*
*
All general-purpose map implementation classes should provide two
* "standard" constructors: a void (no arguments) constructor which creates an
* empty map, and a constructor with a single argument of type Map,
* which creates a new map with the same key-value mappings as its argument.
* In effect, the latter constructor allows the user to copy any map,
* producing an equivalent map of the desired class. There is no way to
* enforce this recommendation (as interfaces cannot contain constructors) but
* all of the general-purpose map implementations in the SDK comply.
*
*
The "destructive" methods contained in this interface, that is, the
* methods that modify the map on which they operate, are specified to throw
* UnsupportedOperationException if this map does not support the
* operation. If this is the case, these methods may, but are not required
* to, throw an UnsupportedOperationException if the invocation would
* have no effect on the map. For example, invoking the {@link #putAll(Map)}
* method on an unmodifiable map may, but is not required to, throw the
* exception if the map whose mappings are to be "superimposed" is empty.
*
*
Some map implementations have restrictions on the keys and values they
* may contain. For example, some implementations prohibit null keys and
* values, and some have restrictions on the types of their keys. Attempting
* to insert an ineligible key or value throws an unchecked exception,
* typically NullPointerException or ClassCastException.
* Attempting to query the presence of an ineligible key or value may throw an
* exception, or it may simply return false; some implementations will exhibit
* the former behavior and some will exhibit the latter. More generally,
* attempting an operation on an ineligible key or value whose completion
* would not result in the insertion of an ineligible element into the map may
* throw an exception or it may succeed, at the option of the implementation.
* Such exceptions are marked as "optional" in the specification for this
* interface.
*
*
This interface is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @version 1.32, 02/02/00
* @see HashMap
* @see TreeMap
* @see Hashtable
* @see SortedMap
* @see Collection
* @see Set
* @since 1.2
*/
public 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.
*
* @return the number of key-value mappings in this map.
*/
public int size();
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings.
*/
public boolean isEmpty();
/**
* 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.)
*
* @param key key whose presence in this map is to be tested.
* @return true if this map contains a mapping for the specified
* key.
*
* @throws ClassCastException if the key is of an inappropriate type for
* this map (optional).
* @throws NullPointerException if the key is null and this map
* does not not permit null keys (optional).
*/
public boolean containsKey(Object key);
/**
* 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.
*
* @param value value whose presence in this map is to be tested.
* @return true if this map maps one or more keys to the
* specified value.
* @throws ClassCastException if the value is of an inappropriate type for
* this map (optional).
* @throws NullPointerException if the value is null and this map
* does not not permit null values (optional).
*/
public boolean containsValue(Object value);
/**
* 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.)
*
* @param key key whose associated value is to be returned.
* @return the value to which this map maps the specified key, or
* null if the map contains no mapping for this key.
*
* @throws ClassCastException if the key is of an inappropriate type for
* this map (optional).
* @throws NullPointerException key is null and this map does not
* not permit null keys (optional).
*
* @see #containsKey(Object)
*/
public Object get(Object key);
/**
* 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 {@link #containsKey(Object) m.containsKey(k)} would return
* true.))
*
* @param key key with which the specified value is to be associated.
* @param value value to be associated with the specified key.
* @return 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.
*
* @throws UnsupportedOperationException if the put operation is
* not supported by this map.
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map.
* @throws IllegalArgumentException if some aspect of this key or value
* prevents it from being stored in this map.
* @throws NullPointerException this map does not permit null
* keys or values, and the specified key or value is
* null.
*/
public Object put(Object key, Object value);
/**
* 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.
*
* @param key key whose mapping is to be removed from the map.
* @return previous value associated with specified key, or null
* if there was no mapping for key.
*
* @throws ClassCastException if the key is of an inappropriate type for
* this map (optional).
* @throws NullPointerException if the key is null and this map
* does not not permit null keys (optional).
* @throws UnsupportedOperationException if the remove method is
* not supported by this map.
*/
public Object remove(Object key);
/**
* 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 {@link #put(Object,Object) 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.
*
* @param t Mappings to be stored in this map.
*
* @throws UnsupportedOperationException if the putAll method is
* not supported by this map.
*
* @throws ClassCastException if the class of a key or value in the
* specified map prevents it from being stored in this map.
*
* @throws IllegalArgumentException some aspect of a key or value in the
* specified map prevents it from being stored in this map.
* @throws NullPointerException the specified map is null, or if
* this map does not permit null keys or values, and the
* specified map contains null keys or values.
*/
public void putAll(Map t);
/**
* Removes all mappings from this map (optional operation).
*
* @throws UnsupportedOperationException clear is not supported by this
* map.
*/
public void clear();
/**
* 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.
*
* @return a set view of the keys contained in this map.
*/
public Set keySet();
/**
* 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.
*
* @return a collection view of the values contained in this map.
*/
public Collection values();
/**
* Returns a set view of the mappings contained in this map. Each element
* in the returned set is a {@link 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.
*
* @return a set view of the mappings contained in this map.
*/
public Set entrySet();
/**
* 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.
*
* @param o object to be compared for equality with this map.
* @return true if the specified object is equal to this map.
*/
public boolean equals(Object o);
/**
* 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.
*
* @return the hash code value for this map.
* @see Map.Entry#hashCode()
* @see Object#hashCode()
* @see Object#equals(Object)
* @see #equals(Object)
*/
public int hashCode();
/**
* A map entry (key-value pair). The Map.entrySet method returns
* a collection-view of the map, whose elements are of this class. The
* only way to obtain a reference to a map entry is from the
* iterator of this collection-view. These Map.Entry objects are
* valid only for the duration of the iteration; more formally,
* the behavior of a map entry is undefined if the backing map has been
* modified after the entry was returned by the iterator, except through
* the iterator's own remove operation, or through the
* setValue operation on a map entry returned by the iterator.
*
* @see Map#entrySet()
* @since 1.2
*/
interface Entry
{
/**
* Returns the key corresponding to this entry.
*
* @return the key corresponding to this entry.
*/
public Object getKey();
/**
* Returns the value corresponding to this entry. If the mapping
* has been removed from the backing map (by the iterator's
* remove operation), the results of this call are undefined.
*
* @return the value corresponding to this entry.
*/
public Object getValue();
/**
* Replaces the value corresponding to this entry with the specified
* value (optional operation). (Writes through to the map.) The
* behavior of this call is undefined if the mapping has already been
* removed from the map (by the iterator's remove operation).
*
* @param value new value to be stored in this entry.
* @return old value corresponding to the entry.
*
* @throws UnsupportedOperationException if the put operation
* is not supported by the backing map.
* @throws ClassCastException if the class of the specified value
* prevents it from being stored in the backing map.
* @throws IllegalArgumentException if some aspect of this value
* prevents it from being stored in the backing map.
* @throws NullPointerException the backing map does not permit
* null values, and the specified value is
* null.
*/
public Object setValue(Object value);
/**
* Compares the specified object with this entry for equality.
* Returns true if the given object is also a map entry and
* the two entries represent the same mapping. More formally, two
* entries e1 and e2 represent the same mapping
* if
* (e1.getKey()==null ?
* e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
* (e1.getValue()==null ?
* e2.getValue()==null : e1.getValue().equals(e2.getValue()))
*
* This ensures that the equals method works properly across
* different implementations of the Map.Entry interface.
*
* @param o object to be compared for equality with this map entry.
* @return true if the specified object is equal to this map
* entry.
*/
public boolean equals(Object o);
/**
* Returns the hash code value for this map entry. The hash code
* of a map entry e is defined to be:
* (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
* (e.getValue()==null ? 0 : e.getValue().hashCode())
*
* This ensures that e1.equals(e2) implies that
* e1.hashCode()==e2.hashCode() for any two Entries
* e1 and e2, as required by the general
* contract of Object.hashCode.
*
* @return the hash code value for this map entry.
* @see Object#hashCode()
* @see Object#equals(Object)
* @see #equals(Object)
*/
public int hashCode();
}
}