import java.util.*;

public class HashMapTest
{
    public static void main(String argv[])
    {
        HashMap hm = new HashMap();
        System.out.println(hm.put("aaa", "111"));
        System.out.println(hm.put("bbb", "222"));
        System.out.println(hm.put("aaa", "444"));
        System.out.println(hm.put("ccc", "333"));    
        System.out.println(hm.put("ccc", null));       
        
        System.out.println("HashMap size : " + hm.size());
        
        Set set = hm.keySet();
        Object []hmKeys = set.toArray();
        for(int i = 0; i < hmKeys.length; i++)
        {
            String key = (String)hmKeys[i];   
            System.out.print(key);
            System.out.print(" - ");
            System.out.println((String)hm.get(key));
        }
    }
}

/**
실행:java HashMapTest
결과:
null
null
111
null
333
HashMap size : 3
ccc - null
bbb - 222
aaa - 444
*/

import java.util.*;

public class Freq

{
    private static final Integer ONE = new Integer(1);

    public static void main(String args[])

    {
        Map m = new TreeMap();

        // Initialize frequency table from command line
        for (int i=0; i < args.length; i++)

        {
            Integer freq = (Integer) m.get(args[i]);
            m.put(args[i], (freq==null ? ONE :
                            new Integer(freq.intValue() + 1)));
        }

        System.out.println(m.size()+" distinct words detected:");
        System.out.println(m);
    }
}

/**
실행:java Freq if it is to be it is up to me to delegate
결과:
8 distinct words detected:
{be=1, delegate=1, if=1, is=2, it=2, me=1, to=3, up=1}
*/

import java.util.*;

public class HashtableTest

{

    public static void main(String argv[])
    {
        Hashtable ht = new Hashtable();
        System.out.println(ht.put("aaa", "111"));
        System.out.println(ht.put("bbb", "222"));
        System.out.println(ht.put("aaa", "444"));
        System.out.println(ht.put("ccc", "333"));    
        
        System.out.println("Hashtable size : " + ht.size());
        
        System.out.println("aaa value : " + (String)ht.get("aaa");
        
    }
}

/**
실행:java HashMapTest
결과:
null
null
111
null
Hashtable size : 3
aaa value : 444
*/