- java.lang.Object
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- java.util.Dictionary<K,V>
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- Direct Known Subclasses:
Hashtable
public abstract class Dictionary<K,V> extends Object
TheDictionaryclass is the abstract parent of any class, such asHashtable, which maps keys to values. Every key and every value is an object. In any oneDictionaryobject, every key is associated with at most one value. Given aDictionaryand a key, the associated element can be looked up. Any non-nullobject can be used as a key and as a value.As a rule, the
equalsmethod should be used by implementations of this class to decide if two keys are the same.NOTE: This class is obsolete.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.
- Since:
- 1.0
- See Also:
Map,Object.equals(java.lang.Object),Object.hashCode(),Hashtable
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Constructor Summary
Constructors Constructor Description Dictionary()Sole constructor.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description abstract Enumeration<V>elements()Returns an enumeration of the values in this dictionary.abstract Vget(Object key)Returns the value to which the key is mapped in this dictionary.abstract booleanisEmpty()Tests if this dictionary maps no keys to value.abstract Enumeration<K>keys()Returns an enumeration of the keys in this dictionary.abstract Vput(K key, V value)Maps the specifiedkeyto the specifiedvaluein this dictionary.abstract Vremove(Object key)Removes thekey(and its correspondingvalue) from this dictionary.abstract intsize()Returns the number of entries (distinct keys) in this dictionary.
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Method Detail
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size
public abstract int size()
Returns the number of entries (distinct keys) in this dictionary.- Returns:
- the number of keys in this dictionary.
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isEmpty
public abstract boolean isEmpty()
Tests if this dictionary maps no keys to value. The general contract for theisEmptymethod is that the result is true if and only if this dictionary contains no entries.- Returns:
trueif this dictionary maps no keys to values;falseotherwise.
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keys
public abstract Enumeration<K> keys()
Returns an enumeration of the keys in this dictionary. The general contract for the keys method is that anEnumerationobject is returned that will generate all the keys for which this dictionary contains entries.- Returns:
- an enumeration of the keys in this dictionary.
- See Also:
elements(),Enumeration
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elements
public abstract Enumeration<V> elements()
Returns an enumeration of the values in this dictionary. The general contract for theelementsmethod is that anEnumerationis returned that will generate all the elements contained in entries in this dictionary.- Returns:
- an enumeration of the values in this dictionary.
- See Also:
keys(),Enumeration
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get
public abstract V get(Object key)
Returns the value to which the key is mapped in this dictionary. The general contract for theisEmptymethod is that if this dictionary contains an entry for the specified key, the associated value is returned; otherwise,nullis returned.- Parameters:
key- a key in this dictionary.nullif the key is not mapped to any value in this dictionary.- Returns:
- the value to which the key is mapped in this dictionary;
- Throws:
NullPointerException- if thekeyisnull.- See Also:
put(java.lang.Object, java.lang.Object)
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put
public abstract V put(K key, V value)
Maps the specifiedkeyto the specifiedvaluein this dictionary. Neither the key nor the value can benull.If this dictionary already contains an entry for the specified
key, the value already in this dictionary for thatkeyis 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 specifiedkeyandvalue, andnullis returned.The
valuecan be retrieved by calling thegetmethod with akeythat is equal to the originalkey.- Parameters:
key- the hashtable key.value- the value.- Returns:
- the previous value to which the
keywas mapped in this dictionary, ornullif the key did not have a previous mapping. - Throws:
NullPointerException- if thekeyorvalueisnull.- See Also:
Object.equals(java.lang.Object),get(java.lang.Object)
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remove
public abstract V remove(Object key)
Removes thekey(and its correspondingvalue) from this dictionary. This method does nothing if thekeyis not in this dictionary.- Parameters:
key- the key that needs to be removed.- Returns:
- the value to which the
keyhad been mapped in this dictionary, ornullif the key did not have a mapping. - Throws:
NullPointerException- ifkeyisnull.
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