/*
 * @(#)Map.java	1.48 04/06/28
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

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.
 *
 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which
 * was a totally abstract class rather than an interface.
 *
 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
 * allow a map's contents to be viewed as a set of keys, collection of values,
 * or set of key-value mappings.  The <i>order</i> 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 <tt>TreeMap</tt> class, make
 * specific guarantees as to their order; others, like the <tt>HashMap</tt>
 * class, do not.
 *
 * <p>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.
 *
 * <p>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 <tt>Map</tt>,
 * 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.
 *
 * <p>The "destructive" methods contained in this interface, that is, the
 * methods that modify the map on which they operate, are specified to throw
 * <tt>UnsupportedOperationException</tt> if this map does not support the
 * operation.  If this is the case, these methods may, but are not required
 * to, throw an <tt>UnsupportedOperationException</tt> 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.
 *
 * <p>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 <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
 * 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.
 *
 * <p>This interface is a member of the 
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * <p>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)
 * contains(Object key)} method says: "returns <tt>true</tt> if and
 * only if this map contain a mapping for a key <tt>k</tt> such that
 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
 * be invoked for any key <tt>k</tt>.  Implementations are free to
 * implement optimizations whereby the <tt>equals</tt> 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.
 *
 * @author  Josh Bloch
 * @version 1.48, 06/28/04
 * @see HashMap
 * @see TreeMap
 * @see Hashtable
 * @see SortedMap
 * @see Collection
 * @see Set
 * @since 1.2
 */
public interface Map<K,V> {
    // Query Operations

    /**
     * Returns the number of key-value mappings in this map.  If the
     * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     *
     * @return the number of key-value mappings in this map.
     */
    int size();

    /**
     * Returns <tt>true</tt> if this map contains no key-value mappings.
     *
     * @return <tt>true</tt> if this map contains no key-value mappings.
     */
    boolean isEmpty();

    /**
     * Returns <tt>true</tt> if this map contains a mapping for the specified
     * key.  More formally, returns <tt>true</tt> if and only if
     * this map contains a mapping for a key <tt>k</tt> such that
     * <tt>(key==null ? k==null : key.equals(k))</tt>.  (There can be
     * at most one such mapping.)
     *
     * @param key key whose presence in this map is to be tested.
     * @return <tt>true</tt> 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 <tt>null</tt> and this map
     *            does not permit <tt>null</tt> keys (optional).
     */
    boolean containsKey(Object key);

    /**
     * Returns <tt>true</tt> if this map maps one or more keys to the
     * specified value.  More formally, returns <tt>true</tt> if and only if
     * this map contains at least one mapping to a value <tt>v</tt> such that
     * <tt>(value==null ? v==null : value.equals(v))</tt>.  This operation
     * will probably require time linear in the map size for most
     * implementations of the <tt>Map</tt> interface.
     *
     * @param value value whose presence in this map is to be tested.
     * @return <tt>true</tt> 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 <tt>null</tt> and this map
     *            does not permit <tt>null</tt> values (optional).
     */
    boolean containsValue(Object value);

    /**
     * Returns the value to which this map maps the specified key.  Returns
     * <tt>null</tt> if the map contains no mapping for this key.  A return
     * value of <tt>null</tt> does not <i>necessarily</i> indicate that the
     * map contains no mapping for the key; it's also possible that the map
     * explicitly maps the key to <tt>null</tt>.  The <tt>containsKey</tt>
     * operation may be used to distinguish these two cases.
     *
     * <p>More formally, if this map contains a mapping from a key
     * <tt>k</tt> to a value <tt>v</tt> such that <tt>(key==null ? k==null :
     * key.equals(k))</tt>, then this method returns <tt>v</tt> otherwise
     * it returns <tt>null</tt>.  (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
     *	       <tt>null</tt> 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 if the key is <tt>null</tt> and this map
     *		  does not permit <tt>null</tt> keys (optional).
     * 
     * @see #containsKey(Object)
     */
    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
     * this key, the old value is replaced by the specified value.  (A map
     * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
     * if {@link #containsKey(Object) m.containsKey(k)} would return
     * <tt>true</tt>.)) 
     *
     * @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 <tt>null</tt>
     *	       if there was no mapping for key.  A <tt>null</tt> return can
     *	       also indicate that the map previously associated <tt>null</tt>
     *	       with the specified key, if the implementation supports
     *	       <tt>null</tt> values.
     * 
     * @throws UnsupportedOperationException if the <tt>put</tt> 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 if this map does not permit <tt>null</tt>
     *            keys or values, and the specified key or value is
     *            <tt>null</tt>.
     */
    V put(K key, V 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 <tt>k</tt> to value <tt>v</tt> such that
     * <code>(key==null ?  k==null : key.equals(k))</code>, that mapping
     * is removed.  (The map can contain at most one such mapping.)
     *
     * <p>Returns the value to which the map previously associated the key, or
     * <tt>null</tt> if the map contained no mapping for this key.  (A
     * <tt>null</tt> return can also indicate that the map previously
     * associated <tt>null</tt> with the specified key if the implementation
     * supports <tt>null</tt> 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 <tt>null</tt>
     *	       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 <tt>null</tt> and this map
     *            does not permit <tt>null</tt> keys (optional).
     * @throws UnsupportedOperationException if the <tt>remove</tt> method is
     *         not supported by this map.
     */
    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 <tt>k</tt> to value <tt>v</tt> 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 <tt>putAll</tt> 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 if the specified map is <tt>null</tt>, or if
     *         this map does not permit <tt>null</tt> keys or values, and the
     *         specified map contains <tt>null</tt> keys or values.
     */
    void putAll(Map<? extends K, ? extends V> t);

    /**
     * Removes all mappings from this map (optional operation).
     *
     * @throws UnsupportedOperationException clear is not supported by this
     * 		  map.
     */
    void clear();


    // Views

    /**
     * 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 (except through the iterator's own <tt>remove</tt>
     * operation), the results of the iteration are undefined.  The set
     * supports element removal, which removes the corresponding mapping from
     * the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
     * <tt>removeAll</tt> <tt>retainAll</tt>, and <tt>clear</tt> operations.
     * It does not support the add or <tt>addAll</tt> operations.
     *
     * @return a set view of the keys contained in this map.
     */
    Set<K> 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 (except through the
     * iterator's own <tt>remove</tt> operation), the results of the
     * iteration are undefined.  The collection supports element removal,
     * which removes the corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations.
     * It does not support the add or <tt>addAll</tt> operations.
     *
     * @return a collection view of the values contained in this map.
     */
    Collection<V> 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
     * (except through the iterator's own <tt>remove</tt> operation, or through
     * the <tt>setValue</tt> operation on a map entry returned by the iterator)
     * the results of the iteration are undefined.  The set supports element
     * removal, which removes the corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
     * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not support
     * the <tt>add</tt> or <tt>addAll</tt> operations.
     *
     * @return a set view of the mappings contained in this map.
     */
    Set<Map.Entry<K, V>> entrySet();

    /**
     * A map entry (key-value pair).  The <tt>Map.entrySet</tt> method returns
     * a collection-view of the map, whose elements are of this class.  The
     * <i>only</i> way to obtain a reference to a map entry is from the
     * iterator of this collection-view.  These <tt>Map.Entry</tt> objects are
     * valid <i>only</i> 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 <tt>setValue</tt> operation on the map entry.
     *
     * @see Map#entrySet()
     * @since 1.2
     */
    interface Entry<K,V> {
    	/**
	 * Returns the key corresponding to this entry.
	 *
	 * @return the key corresponding to this entry.
         * @throws IllegalStateException implementations may, but are not
         *         required to, throw this exception if the entry has been
         *         removed from the backing map
	 */
	K getKey();

    	/**
	 * Returns the value corresponding to this entry.  If the mapping
	 * has been removed from the backing map (by the iterator's
	 * <tt>remove</tt> operation), the results of this call are undefined.
	 *
	 * @return the value corresponding to this entry.
         * @throws IllegalStateException implementations may, but are not
         *         required to, throw this exception if the entry has been
         *         removed from the backing map
	 */
	V 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 <tt>remove</tt> operation).
	 *
	 * @param value new value to be stored in this entry.
	 * @return old value corresponding to the entry.
         * 
	 * @throws UnsupportedOperationException if the <tt>put</tt> 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 if the backing map does not permit
	 *	      <tt>null</tt> values, and the specified value is
	 *	      <tt>null</tt>.
         * @throws IllegalStateException implementations may, but are not
         *         required to, throw this exception if the entry has been
         *         removed from the backing map
         */
	V setValue(V value);

	/**
	 * Compares the specified object with this entry for equality.
	 * Returns <tt>true</tt> if the given object is also a map entry and
	 * the two entries represent the same mapping.  More formally, two
	 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
	 * if<pre>
         *     (e1.getKey()==null ?
         *      e2.getKey()==null : e1.getKey().equals(e2.getKey()))  &&
         *     (e1.getValue()==null ?
         *      e2.getValue()==null : e1.getValue().equals(e2.getValue()))
         * </pre>
	 * This ensures that the <tt>equals</tt> method works properly across
	 * different implementations of the <tt>Map.Entry</tt> interface.
	 *
	 * @param o object to be compared for equality with this map entry.
	 * @return <tt>true</tt> 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 <tt>e</tt> is defined to be: <pre>
	 *     (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
	 *     (e.getValue()==null ? 0 : e.getValue().hashCode())
         * </pre>
	 * This ensures that <tt>e1.equals(e2)</tt> implies that
	 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
	 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
	 * contract of <tt>Object.hashCode</tt>.
	 *
	 * @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
     * <tt>true</tt> if the given object is also a map and the two Maps
     * represent the same mappings.  More formally, two maps <tt>t1</tt> and
     * <tt>t2</tt> represent the same mappings if
     * <tt>t1.entrySet().equals(t2.entrySet())</tt>.  This ensures that the
     * <tt>equals</tt> method works properly across different implementations
     * of the <tt>Map</tt> interface.
     *
     * @param o object to be compared for equality with this map.
     * @return <tt>true</tt> 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 hashCodes of each entry in the map's
     * entrySet view.  This ensures that <tt>t1.equals(t2)</tt> implies
     * that <tt>t1.hashCode()==t2.hashCode()</tt> for any two maps
     * <tt>t1</tt> and <tt>t2</tt>, 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)
     */
    int hashCode();
}