java.util.Dictionary Maven / Gradle / Ivy
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package java.util;
/**
* The Dictionary class is the abstract parent of any
* class, such as Hashtable, which maps keys to values.
* Every key and every value is an object. In any one Dictionary
* object, every key is associated with at most one value. Given a
* Dictionary and a key, the associated element can be looked up.
* Any non-null object can be used as a key and as a value.
*
* As a rule, the equals method should be used by
* implementations of this class to decide if two keys are the same.
*
* NOTE: This class is obsolete. New implementations should
* implement the Map interface, rather than extending this class.
*
* @author unascribed
* @see java.util.Map
* @see java.lang.Object#equals(java.lang.Object)
* @see java.lang.Object#hashCode()
* @see java.util.Hashtable
* @since JDK1.0
*/
public abstract
class Dictionary {
/**
* 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.
*/
abstract public int size();
/**
* Tests if this dictionary maps no keys to value. The general contract
* for the isEmpty method is that the result is true if and only
* if this dictionary contains no entries.
*
* @return true if this dictionary maps no keys to values;
* false otherwise.
*/
abstract public boolean isEmpty();
/**
* Returns an enumeration of the keys in this dictionary. The general
* contract for the keys method is that an 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
*/
abstract public Enumeration keys();
/**
* Returns an enumeration of the values in this dictionary. The general
* contract for the elements method is that an
* 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
*/
abstract public Enumeration elements();
/**
* Returns the value to which the key is mapped in this dictionary.
* The general contract for the isEmpty method is that if this
* dictionary contains an entry for the specified key, the associated
* value is returned; otherwise, null is returned.
*
* @return the value to which the key is mapped in this dictionary;
* @param key a key in this dictionary.
* null if the key is not mapped to any value in
* this dictionary.
* @exception NullPointerException if the key is null.
* @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
*/
abstract public V get(Object key);
/**
* Maps the specified key to the specified
* value in this dictionary. Neither the key nor the
* value can be null.
*
* If this dictionary already contains an entry for the specified
* key, the value already in this dictionary for that
* key is returned, after modifying the entry to contain the
* new element.
If this dictionary does not already have an entry
* for the specified key, an entry is created for the
* specified key and value, and null is
* returned.
*
* The value can be retrieved by calling the
* get method with a key that is equal to
* the original key.
*
* @param key the hashtable key.
* @param value the value.
* @return the previous value to which the key was mapped
* in this dictionary, or null if the key did not
* have a previous mapping.
* @exception NullPointerException if the key or
* value is null.
* @see java.lang.Object#equals(java.lang.Object)
* @see java.util.Dictionary#get(java.lang.Object)
*/
abstract public V put(K key, V value);
/**
* Removes the key (and its corresponding
* value) from this dictionary. This method does nothing
* if the key is not in this dictionary.
*
* @param key the key that needs to be removed.
* @return the value to which the key had been mapped in this
* dictionary, or null if the key did not have a
* mapping.
* @exception NullPointerException if key is null.
*/
abstract public V remove(Object key);
}