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 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 JDK 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. - * - *
Many methods in Collections Framework interfaces are defined
- * in terms of the {@link Object#equals(Object) equals} method. For
- * example, the specification for the {@link #containsKey(Object)
- * containsKey(Object key)} method says: "returns true if and
- * only if this map contains a mapping for a key k such that
- * (key==null ? k==null : key.equals(k))." This specification should
- * not be construed to imply that invoking Map.containsKey
- * with a non-null argument key will cause key.equals(k) to
- * be invoked for any key k. Implementations are free to
- * implement optimizations whereby the equals invocation is avoided,
- * for example, by first comparing the hash codes of the two keys. (The
- * {@link Object#hashCode()} specification guarantees that two objects with
- * unequal hash codes cannot be equal.) More generally, implementations of
- * the various Collections Framework interfaces are free to take advantage of
- * the specified behavior of underlying {@link Object} methods wherever the
- * implementor deems it appropriate.
- *
- * @param More formally, if this map contains a mapping from a key
- * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
- * key.equals(k))}, then this method returns {@code v}; otherwise
- * it returns {@code null}. (There can be at most one such mapping.)
- *
- * If this map permits null values, then a return value of
- * {@code 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 {@code null}. The {@link #containsKey
- * containsKey} operation may be used to distinguish these two cases.
- *
- * @param key the key whose associated value is to be returned
- * @return the value to which the specified key is mapped, or
- * {@code null} if this map contains no mapping for the key
- * @throws ClassCastException if the key is of an inappropriate type for
- * this map
- * (optional)
- * @throws NullPointerException if the specified key is null and this map
- * does not permit null keys
- * (optional)
- */
- V get(Object key);
-
- // Modification Operations
-
- /**
- * Associates the specified value with the specified key in this map
- * (optional operation). If the map previously contained a mapping for
- * the 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 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 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 NullPointerException if the specified key or value is null
- * and this map does not permit null keys or values
- * @throws IllegalArgumentException if some property of the specified key
- * or value prevents it from being stored in this map
- */
- V put(K key, V value);
-
- /**
- * Removes the mapping for a 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
- * Returns the value to which this map previously associated the key,
- * or null if the map contained no mapping for the key.
- *
- * If this map permits null values, then a return value of
- * null does not necessarily indicate that the map
- * contained no mapping for the key; it's also possible that the map
- * explicitly mapped the key to null.
- *
- * 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 the previous value associated with key, or
- * null if there was no mapping for key.
- * @throws UnsupportedOperationException if the remove operation
- * is not supported by this map
- * @throws ClassCastException if the key is of an inappropriate type for
- * this map
- * (optional)
- * @throws NullPointerException if the specified key is null and this
- * map does not permit null keys
- * (optional)
- */
- V remove(Object key);
-
-
- // Bulk Operations
-
- /**
- * 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 undefined if the
- * specified map is modified while the operation is in progress.
- *
- * @param m mappings to be stored in this map
- * @throws UnsupportedOperationException if the putAll operation
- * 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 NullPointerException if 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
- * @throws IllegalArgumentException if some property of a key or value in
- * the specified map prevents it from being stored in this map
- */
- void putAll(Map m);
-
- /**
- * Removes all of the mappings from this map (optional operation).
- * The map will be empty after this call returns.
- *
- * @throws UnsupportedOperationException if the clear operation
- * is not supported by this map
- */
- void clear();
-
-
- // Views
-
- /**
- * Returns a {@link 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 (except through
- * the iterator's own remove operation), 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
- */
- Set(key==null ? k==null : key.equals(k)), that mapping
- * is removed. (The map can contain at most one such mapping.)
- *
- *
- * (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
- */
- 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)
- */
- int hashCode();
- }
-
- // Comparison and hashing
-
- /**
- * 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 m1 and
- * m2 represent the same mappings if
- * m1.entrySet().equals(m2.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
- */
- 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 hash codes of each entry in the map's
- * entrySet() view. This ensures that m1.equals(m2)
- * implies that m1.hashCode()==m2.hashCode() for any two maps
- * m1 and m2, as required by the general contract of
- * {@link Object#hashCode}.
- *
- * @return the hash code value for this map
- * @see Map.Entry#hashCode()
- * @see Object#equals(Object)
- * @see #equals(Object)
- */
- int hashCode();
-
-}