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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;

/**
 * The {@code Dictionary} class is the abstract parent of any
 * class, such as {@code Hashtable}, which maps keys to values.
 * Every key and every value is an object. In any one {@code Dictionary}
 * object, every key is associated with at most one value. Given a
 * {@code Dictionary} and a key, the associated element can be looked up.
 * Any non-{@code null} object can be used as a key and as a value.
 * <p>
 * As a rule, the {@code equals} method should be used by
 * implementations of this class to decide if two keys are the same.
 * <p>
 * <strong>NOTE: This class is obsolete. New implementations should
 * implement the Map interface, rather than extending this class.</strong>
 *
 * @author unascribed
 * @see java.util.Map
 * @see java.lang.Object#equals(java.lang.Object)
 * @see java.lang.Object#hashCode()
 * @see java.util.Hashtable
 * @since 1.0
 */
public abstract
class Dictionary<K,V> {
 /**
 * Sole constructor. (For invocation by subclass constructors, typically
 * implicit.)
 */
 public Dictionary() {
 }

 /**
 * Returns the number of entries (distinct keys) in this dictionary.
 *
 * @return the number of keys in this dictionary.
 */
 public abstract int size();

 /**
 * Tests if this dictionary maps no keys to value. The general contract
 * for the {@code isEmpty} method is that the result is true if and only
 * if this dictionary contains no entries.
 *
 * @return {@code true} if this dictionary maps no keys to values;
 * {@code false} otherwise.
 */
 public abstract boolean isEmpty();

 /**
 * Returns an enumeration of the keys in this dictionary. The general
 * contract for the keys method is that an {@code Enumeration} object
 * is returned that will generate all the keys for which this dictionary
 * contains entries.
 *
 * @return an enumeration of the keys in this dictionary.
 * @see java.util.Dictionary#elements()
 * @see java.util.Enumeration
 */
 public abstract Enumeration<K> keys();

 /**
 * Returns an enumeration of the values in this dictionary. The general
 * contract for the {@code elements} method is that an
 * {@code Enumeration} is returned that will generate all the elements
 * contained in entries in this dictionary.
 *
 * @return an enumeration of the values in this dictionary.
 * @see java.util.Dictionary#keys()
 * @see java.util.Enumeration
 */
 public abstract Enumeration<V> elements();

 /**
 * Returns the value to which the key is mapped in this dictionary.
 * The general contract for the {@code isEmpty} method is that if this
 * dictionary contains an entry for the specified key, the associated
 * value is returned; otherwise, {@code null} is returned.
 *
 * @return the value to which the key is mapped in this dictionary;
 * @param key a key in this dictionary.
 * {@code null} if the key is not mapped to any value in
 * this dictionary.
 * @exception NullPointerException if the {@code key} is {@code null}.
 * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
 */
 public abstract V get(Object key);

 /**
 * Maps the specified {@code key} to the specified
 * {@code value} in this dictionary. Neither the key nor the
 * value can be {@code null}.
 * <p>
 * If this dictionary already contains an entry for the specified
 * {@code key}, the value already in this dictionary for that
 * {@code key} is returned, after modifying the entry to contain the
 * new element. <p>If this dictionary does not already have an entry
 * for the specified {@code key}, an entry is created for the
 * specified {@code key} and {@code value}, and {@code null} is
 * returned.
 * <p>
 * The {@code value} can be retrieved by calling the
 * {@code get} method with a {@code key} that is equal to
 * the original {@code key}.
 *
 * @param key the hashtable key.
 * @param value the value.
 * @return the previous value to which the {@code key} was mapped
 * in this dictionary, or {@code null} if the key did not
 * have a previous mapping.
 * @exception NullPointerException if the {@code key} or
 * {@code value} is {@code null}.
 * @see java.lang.Object#equals(java.lang.Object)
 * @see java.util.Dictionary#get(java.lang.Object)
 */
 public abstract V put(K key, V value);

 /**
 * Removes the {@code key} (and its corresponding
 * {@code value}) from this dictionary. This method does nothing
 * if the {@code key} is not in this dictionary.
 *
 * @param key the key that needs to be removed.
 * @return the value to which the {@code key} had been mapped in this
 * dictionary, or {@code null} if the key did not have a
 * mapping.
 * @exception NullPointerException if {@code key} is {@code null}.
 */
 public abstract V remove(Object key);
}