java : hashmap 사용법 & 소팅

package main.java.com;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.TreeSet;
import java.util.Vector;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class job {

 private static Log logger = LogFactory.getLog(job.class);

 public static void main(String[] args) {
  // TODO Auto-generated method stub
  HashMap<String,String> hm = new HashMap<String, String>();
  
  
  hm.put("01", "01String");
  hm.put("02", "02String");
  hm.put("03", "03String");
  hm.put("04", "04String");
  hm.put("05", "05String");
  hm.put("06", "06String");
  
  
  
  Iterator<String> iter = hm.keySet().iterator();
  while(iter.hasNext())
  {
   String cnt = iter.next();
   logger.debug(hm.get(cnt));
  }
  
  // Sort hashtable.
        Vector v = new Vector(hm.keySet());
        Collections.sort(v);
       
        for (Enumeration e = v.elements(); e.hasMoreElements();) {
            String key = (String)e.nextElement();
            String val = (String)hm.get(key);             
            System.out.println("Key: " + key + " Val: " + val);
       }
       
       
       
       
        HashMap<Integer,VO> hm2 = new HashMap<Integer, VO>();
        for(int i=0;i<1000;i++)
        {
         VO v1 = new VO();
         v1.setA1("a"+"_"+i);
         v1.setA2("b"+"_"+i);
         v1.setA3("c"+"_"+i);
         hm2.put(i, v1);
        }
       
       
        logger.debug(hm2.get(100).getA1());
       
 }
 

}

class VO{
 private String a1 = "";
 private String a2 = "";
 private String a3 = "";
 
 public String getA1()
 {
  return this.a1;
 }
 
 public String getA2()
 {
  return this.a2;
 }
 
 public String getA3()
 {
  return this.a3;
 }
 
 public void setA1(String a1)
 {
  this.a1 = a1;
 }
 
 public void setA2(String a2)
 {
  this.a2 = a2;
 }
 
 public void setA3(String a3)
 {
  this.a3 = a3;
 }
 
 
 
 
 
 
}