• Map map = new HashMap()
• Set set = map.entrySet();
• Iterator it = set.iterator();
• map.put(arg0, arg1)
• Arrays to Map.put with for loop
• Map.Entry(), getKey(), getValue

1. both inserting and searching data are quick.
   1.  HashMap is unsynchronized and Hashtable is synchronized.
   2.  HashMap is the faster than Hashtable.
   3. HashMap allows null where Hashtable does not allow null.
   4. If you need to maintain map keys in an ordered fashion, you should use TreeMap.
   5. Map has get and put, where as Set does not

* The Collection interface is a group of objects, with duplicates allowed.
* The Set interface extends Collection but  won't allow duplicate values.
* The List interface extends Collection, allows duplicates, and introduces positional
indexing.
* The Map interface extends neither Set nor Collection.

    constructors
    HashMap() 	                        default
    HashMap(Map m) 			takes map object
    HashMap(int capacity) 		size
    HashMap(int capacity, float fill)	
    ---------------Methods----------
    boolean equals(Object obj)	returns true 
                                when object equals
                                to Map.Entry key 
    
    Object getKey
    Object getValue
    int hashCode
    Object seValue(Object obj)   sets this map.
                                Entry to object value.
    

import java.io.*;
import java.util.List;
import java.util.Arrays;// to use arrays
import java.util.*;// Arrays.sort
import java.util.Enumeration;
public class Test_This {
public static void main(String[] args) throws IOException{
// TODO Auto-generated method stub
Process p1 = new Process();
p1.method_1();
}
}
class Process
{
String first[] = {"Java","A+","C#","XML","JSP","PHP","Z", "C#"};
public Process()
{
System.out.println("Default) constructor");
}
public void method_1()
{
Map map = new HashMap();
for(int i = 0; i < first.length; i++)
{
//map.put(arg0, arg1)
map.put(("key " + i), first[i]);
}
System.out.println(map);
Set set = map.entrySet();
Iterator it = set.iterator();
System.out.println("-----Using Iteration----");
while (it.hasNext())
{
Map.Entry me = (Map.Entry)it.next();
System.out.print(me.getKey()+ " : ");
System.out.print(me.getValue());
System.out.println();
}
}
}