Hashtable

java.lang.Object
- java.util.Dictionary
- - java.util.Hashtable

All Implemented Interfaces:

Serializable, Cloneable, Map

Direct Known Subclasses:

ClassFile.UtfPool, FieldHandler, ImageCache, Properties
```
public class Hashtable
extends Dictionary
implements Cloneable, Serializable, Map
```
A Hashtable is an implementation of a Map. This is a collection that associates Object values with Object keys. You search for an object in the Map by using the key.

See Also:

Serialized Form

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  Map.Entry

Field Summary
- Fields inherited from interface java.io.Serializable
  serialVersionUID

Constructor Summary

Constructors
Constructor and Description
`Hashtable()` Constructs a new hashtable with the default initial capacity and a default load factor of 0.75
`Hashtable(int initialCapacity)` Constructs a new hashtable with the specified initial capacity and a default load factor of 0.75
`Hashtable(int initialCapacity, float loadFactor)` Constructs a hashtable with the specified initial capacity and the specified load factor.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`clear()` Remove all entries from this Map (optional operation).
`Object`	`clone()` Create a field for field copy of this Object if this Object implements the Cloneable interface.
`boolean`	`contains(Object value)`
`boolean`	`containsKey(Object key)` Returns true if this contains a mapping for the given key.
`boolean`	`containsValue(Object value)` Returns true if this contains at least one mapping with the given value.
`Enumeration`	`elements()` Returns an Enumeration of the values in this Dictionary.
`Set`	`entrySet()` Returns a set view of the mappings in this Map.
`Object`	`get(Object key)` Returns the value associated with the supplied key, or null if no such value exists.
`boolean`	`isEmpty()` Returns true when there are no elements in this Dictionary.
`Enumeration`	`keys()` Returns an Enumeration of the keys in this Dictionary
`Set`	`keySet()` Returns a set view of the keys in this Map.
`Object`	`put(Object key, Object value)` Inserts a new value into this Dictionary, located by the supplied key.
`void`	`putAll(Map m)` Copies all entries of the given map to this one (optional operation).
`protected void`	`rehash()`
`Object`	`remove(Object key)` Removes from the Dictionary the value located by the given key.
`int`	`size()` Returns the number of values currently in this Dictionary.
`String`	`toString()` Returns a string representation of this `Hashtable` object in the form of a set of entries, enclosed in braces and separated by the ASCII characters "`,` " (comma and space).
`Collection`	`values()` Returns a collection (or bag) view of the values in this Map.

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map
equals, hashCode

- Constructor Detail
  - Hashtable
```
public Hashtable(int initialCapacity,
                 float loadFactor)
```
    Constructs a hashtable with the specified initial capacity and the specified load factor.
  - Hashtable
```
public Hashtable(int initialCapacity)
```
    Constructs a new hashtable with the specified initial capacity and a default load factor of 0.75
  - Hashtable
```
public Hashtable()
```
    Constructs a new hashtable with the default initial capacity and a default load factor of 0.75
- Method Detail
  - clone
```
public Object clone()
```
    Description copied from class: Object
    
    Create a field for field copy of this Object if this Object implements the Cloneable interface.
    
    Overrides:
    
    clone in class Object
    
    Returns:
    
    A clone of this Object.
  - size
```
public int size()
```
    Description copied from class: Dictionary
    
    Returns the number of values currently in this Dictionary.
    
    Specified by:
    
    size in interface Map
    
    Specified by:
    
    size in class Dictionary
    
    Returns:
    
    the number of keys in the Dictionary
  - isEmpty
```
public boolean isEmpty()
```
    Description copied from class: Dictionary
    
    Returns true when there are no elements in this Dictionary.
    
    Specified by:
    
    isEmpty in interface Map
    
    Specified by:
    
    isEmpty in class Dictionary
    
    Returns:
    
    size() == 0
  - contains
```
public boolean contains(Object value)
```
  - containsKey
```
public boolean containsKey(Object key)
```
    Description copied from interface: Map
    
    Returns true if this contains a mapping for the given key.
    
    Specified by:
    
    containsKey in interface Map
    
    Parameters:
    
    key - the key to search for
    
    Returns:
    
    true if the map contains the key
  - remove
```
public Object remove(Object key)
```
    Description copied from class: Dictionary
    
    Removes from the Dictionary the value located by the given key. A null return safely means that the key was not mapped in the Dictionary.
    
    Specified by:
    
    remove in interface Map
    
    Specified by:
    
    remove in class Dictionary
    
    Parameters:
    
    key - the key used to locate the value to be removed
    
    Returns:
    
    the value associated with the removed key
  - put
```
public Object put(Object key,
                  Object value)
```
    Description copied from class: Dictionary
    
    Inserts a new value into this Dictionary, located by the supplied key. Dictionary does not support null keys or values, so a null return can safely be interpreted as adding a new key.
    
    Specified by:
    
    put in interface Map
    
    Specified by:
    
    put in class Dictionary
    
    Parameters:
    
    key - the key which locates the value
    
    value - the value to put into the Dictionary
    
    Returns:
    
    the previous value of the key, or null if there was none
    
    See Also:
    
    Dictionary.get(Object)
  - clear
```
public void clear()
```
    Description copied from interface: Map
    
    Remove all entries from this Map (optional operation).
    
    Specified by:
    
    clear in interface Map
  - get
```
public Object get(Object key)
```
    Description copied from class: Dictionary
    
    Returns the value associated with the supplied key, or null if no such value exists. Since Dictionaries are not allowed null keys or elements, a null result always means the key is not present.
    
    Specified by:
    
    get in interface Map
    
    Specified by:
    
    get in class Dictionary
    
    Parameters:
    
    key - the key to use to fetch the value
    
    Returns:
    
    the mapped value
    
    See Also:
    
    Dictionary.put(Object, Object)
  - rehash
```
protected void rehash()
```
  - elements
```
public Enumeration elements()
```
    Description copied from class: Dictionary
    
    Returns an Enumeration of the values in this Dictionary.
    
    Specified by:
    
    elements in class Dictionary
    
    Returns:
    
    an Enumeration of the values
    
    See Also:
    
    Dictionary.keys()
  - keys
```
public Enumeration keys()
```
    Description copied from class: Dictionary
    
    Returns an Enumeration of the keys in this Dictionary
    
    Specified by:
    
    keys in class Dictionary
    
    Returns:
    
    an Enumeration of the keys
    
    See Also:
    
    Dictionary.elements()
  - toString
```
public String toString()
```
    Returns a string representation of this Hashtable object in the form of a set of entries, enclosed in braces and separated by the ASCII characters ", " (comma and space). Each entry is rendered as the key, an equals sign =, and the associated element, where the toString method is used to convert the key and element to strings.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    
    a string representation of this hashtable
    
    Since:
    
    2018.06
  - containsValue
```
public boolean containsValue(Object value)
```
    Description copied from interface: Map
    
    Returns true if this contains at least one mapping with the given value. In other words, returns true if a value v exists where (value == null ? v == null : value.equals(v)). This usually requires linear time.
    
    Specified by:
    
    containsValue in interface Map
    
    Parameters:
    
    value - the value to search for
    
    Returns:
    
    true if the map contains the value
  - entrySet
```
public Set entrySet()
```
    Description copied from interface: Map
    
    Returns a set view of the mappings in this Map. Each element in the set is a Map.Entry. The set is backed by the map, so that changes in one show up in the other. Modifications made while an iterator is in progress cause undefined behavior. If the set supports removal, these methods remove the underlying mapping from the map: Iterator.remove, Set.remove, removeAll, retainAll, and clear. Element addition, via add or addAll, is not supported via this set.
    
    Specified by:
    
    entrySet in interface Map
    
    Returns:
    
    the set view of all mapping entries
    
    See Also:
    
    Map.Entry
  - keySet
```
public Set keySet()
```
    Description copied from interface: Map
    
    Returns a set view of the keys in this Map. The set is backed by the map, so that changes in one show up in the other. Modifications made while an iterator is in progress cause undefined behavior. If the set supports removal, these methods remove the underlying mapping from the map: Iterator.remove, Set.remove, removeAll, retainAll, and clear. Element addition, via add or addAll, is not supported via this set.
    
    Specified by:
    
    keySet in interface Map
    
    Returns:
    
    the set view of all keys
  - putAll
```
public void putAll(Map m)
```
    Description copied from interface: Map
    
    Copies all entries of the given map to this one (optional operation). If the map already contains a key, its value is replaced.
    
    Specified by:
    
    putAll in interface Map
    
    Parameters:
    
    m - the mapping to load into this map
    
    See Also:
    
    Map.put(Object, Object)
  - values
```
public Collection values()
```
    Description copied from interface: Map
    
    Returns a collection (or bag) view of the values in this Map. The collection is backed by the map, so that changes in one show up in the other. Modifications made while an iterator is in progress cause undefined behavior. If the collection supports removal, these methods remove the underlying mapping from the map: Iterator.remove, Collection.remove, removeAll, retainAll, and clear. Element addition, via add or addAll, is not supported via this collection.
    
    Specified by:
    
    values in interface Map
    
    Returns:
    
    the collection view of all values

Class Hashtable

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Field Summary

Fields inherited from interface java.io.Serializable

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Constructor Detail

Hashtable

Hashtable

Hashtable

Method Detail

clone

size

isEmpty

contains

containsKey

remove

put

clear

get

rehash

elements

keys

toString

containsValue

entrySet

keySet

putAll

values