java.util.Dictionary
Dictionary
is an object that associates elements with keys. Every key and
every element is an object. In any one Dictionary
, every key is associated at
most one element. Given a Dictionary
and a key, the associated element can be
looked up.
public abstract classAs a rule, theDictionary
{ abstract public intsize
(); abstract public booleanisEmpty
(); abstract public Objectget
(Object key) throws NullPointerException; abstract public Objectput
(Object key, Object element) throws NullPointerException; abstract public Objectremove
(Object key) throws NullPointerException; abstract public Enumerationkeys
(); abstract public Enumerationelements
(); }
equals
method (§20.1.3) should be used by implementations of the class Dictionary
to decide whether two keys are the same.21.4.1 abstract public int
size
()
The general contract for the size
method is that it returns the number of entries
(distinct keys) in this dictionary.
21.4.2 abstract public boolean
isEmpty
()
The general contract for the isEmpty
method is that the result is true
if and only
if this dictionary contains no entries.
21.4.3 abstract public Object
get
(Object key)
throws NullPointerException
The general contract for the isEmpty
method is that if this dictionary contains an
entry for the specified key
, the associated element is returned; otherwise, null
is
returned.
If the key
is null
, a NullPointerException
is thrown.
21.4.4 abstract public Object
put
(Object key, Object element)
throws NullPointerException
The general contract for the put
method is that it adds an entry to this dictionary.
If this dictionary already contains an entry for the specified key
, the element 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 element
, and null
is returned.
If the key
or the element
is null
, a NullPointerException
is thrown.
21.4.5 abstract public Object
remove
(Object key)
throws NullPointerException
The general contract for the remove
method is that it removes an entry from this
dictionary.
If this dictionary contains an entry for the specified key
, the element in this dictionary for that key
is returned, after removing the entry from this dictionary.
If this dictionary does not already have an entry for the specified key
, null
is returned.
If the key
is null
, a NullPointerException
is thrown.
21.4.6 abstract public Enumeration
keys
()
The general contract for the keys
method is that an Enumeration
(§21.1) is
returned that will generate all the keys for which this dictionary contains entries.
21.4.7 abstract public Enumeration
elements
()
The general contract for the elements
method is that an Enumeration
(§21.1) is
returned that will generate all the elements contained in entries in this dictionary.
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