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public class java.util.Hashtable extends java.util.Dictionary (I-§3.3) implements java.lang.Cloneable (I-§1.22) { // Constructors public Hashtable(); §3.4.1 public Hashtable(int initialCapacity); §3.4.2 public Hashtable(int initialCapacity, float loadFactor); §3.4.3 // Methods public void clear(); §3.4.4 public Object clone(); §3.4.5 public boolean contains(Object value); §3.4.6 public boolean containsKey(Object key); §3.4.7 public Enumeration elements(); §3.4.8 public Object get(Object key); §3.4.9 public boolean isEmpty(); §3.4.10 public Enumeration keys(); §3.4.11 public Object put(Object key, Object value); §3.4.12 protected void rehash(); §3.4.13 public Object remove(Object key); §3.4.14 public int size(); §3.4.15 public String toString(); §3.4.16 }This class implements a hash table, which maps keys to values. Any non-null object can be used as a key or as a value.
To successfully store and retrieve objects from a hash table, the objects used as keys must implement the hashCode method (I-§1.12.6) and the equals method (I-§1.12.3).
An instance of Hashtable has two parameters that affect its efficiency: its capacity and its load factor. The load factor should be between 0.0 and 1.0. When the number of entries in the hash table exceeds the product of the load factor and the current capacity, the capacity is increased by calling the rehash method (I-§3.4.13). Larger load factors use memory more efficiently, at the expense of larger expected time per lookup.
This example creates a hashtable of numbers. It uses the names of the numbers as keys:
Hashtable numbers = new Hashtable();
numbers.put("one", new Integer(1));
numbers.put("two", new Integer(2));
numbers.put("three", new Integer(3));
Integer n = (Integer)numbers.get("two");
if (n != null) {
System.out.println("two = " + n);
}
public Hashtable()
public Hashtable(int initialCapacity)
initialCapacity
-
the initial capacity of the hash table
public
Hashtable(int initialCapacity, float loadFactor)
initialCapacity
-
the initial size of the hashtable
loadFactor
-
a number between 0.0 and 1.0,
public void clear()
public Object clone()
public boolean contains(Object value)
value
-
a value to search for
public boolean containsKey(Object key)
key
-
possible key
public Enumeration elements()
public Object get(Object key)
key
-
a key in the hash table
public boolean isEmpty()
public Enumeration keys()
public Object put(Object key, Object value)
key
-
the hashtable key
value
-
the value
protected void rehash()
public Object remove(Object key)
key
-
the key that needs to be removed
public int size()
public String toString()
Packages This Package Prev Next IndexJava API Document (HTML generated by dkramer on April 22, 1996)