java Hastable使用

jdk：http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Hashtable.html

  Hashtable numbers = new Hashtable();
     numbers.put("one", new Integer(1));
     numbers.put("two", new Integer(2));
     numbers.put("three", new Integer(3));
 

To retrieve a number, use the following code:

     Integer n = (Integer)numbers.get("two");
     if (n != null) {
         System.out.println("two = " + n);
     }

Enumeration keys()
    Returns an enumeration of the keys in this hashtable.

Set keySet()
           Returns a Set view of the keys contained in this Hashtable.
Object put(Object key, Object value)
  Maps the specified key to the specified value in this hashtable.

Collection values()
  Returns a Collection view of the values contained in this Hashtable.

Object clone()
　　Creates a shallow copy of this hashtable.
boolean contains(Object value)
　　Tests if some key maps into the specified value in this hashtable.
boolean containsKey(Object key)
　　Tests if the specified object is a key in this hashtable.
boolean containsValue(Object value)
　　Returns true if this Hashtable maps one or more keys to this value.

contains containskey区别，没什么区别，只不过containskey是很早以前的方法，contains是collection采用的方法。

官方说法：

contains:Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the collections framework).

遍历方法：

1.

private static void test() {
        Hashtable<String,String> table = new Hashtable<String,String>();
        table.put("1", "hello");
        table.put("2", "world!");
        Iterator i = table.entrySet().iterator();
        while(i.hasNext()){
            Entry entry = (Entry) i.next();
            System.out.println(entry.getKey()+"=>"+entry.getValue());
        }
    } 

table.entrySet返回的是一个set集合。集合里的元素为Entry。

第二种方法：

public class Hashtable1 {
    Hashtable<String,String> table=new Hashtable<String,String>();

    public void retrieve()
    {
        table.put("1","hello");
        table.put("2","world!");

        Enumeration e=table.keys();
        while(e.hasMoreElements())
        {
            Object elem=e.nextElement();
            System.out.println(elem+"=>"+table.get(elem));
        }
    }

Enumeration遍历方法：

public interface Enumeration

An object that implements the Enumeration interface generates a series of elements, one at a time. Successive calls to the nextElement method return successive elements of the series.

For example, to print all elements of a vector v:

     for (Enumeration e = v.elements() ; e.hasMoreElements() ;) {
         System.out.println(e.nextElement());
     }

深入：

http://www.blogjava.net/fhtdy2004/archive/2009/07/03/285330.html

http://blog.csdn.net/teedry/article/details/4280034