Java日付時刻関数について

package test;

import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;

public class SQLDate {

    public static void main(String[] args){
        
        System.out.println(System.currentTimeMillis());        //  ：1244711626453
        
        java.util.Date date1 = new java.util.Date();
        System.out.println(date1.toString());    //  : Thu Jun 11 16:27:57 CST 2009
        
        //java.sql.Date extends java.util.Date
        java.sql.Date date2 = new java.sql.Date(System.currentTimeMillis());
        System.out.println(date2.toString());    //  : 2009-06-11
        
        java.sql.Date date3 = new java.sql.Date(date1.getTime());
        System.out.println(date3.toString());    //  ：2009-06-11
        
        //Timestamp extends java.util.Date
        Timestamp stamp1 = new Timestamp(System.currentTimeMillis());
        System.out.println(stamp1.toString());    //  ： 2009-06-11 16:27:57.75
        
        Timestamp stamp2 = new Timestamp(date1.getTime());
        System.out.println(stamp2.toString());    //  ：2009-06-11 16:52:56.171

        //              
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        //format(java.util.Date date), Timestamp java.util.Date   
        String timeStr =  sdf.format(stamp1);    
        System.out.println(timeStr);    //  ：2009/06/11 16:52:56
        
        //SimpleDateFormat extends DateFormat，DateFormat    
        DateFormat df = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        String timeStr2 = df.format(date1);
        String timeStr3 = df.format(date2);
        System.out.println(timeStr2);    //  ：2009/06/11 16:52:56
        System.out.println(timeStr3);    //  ： 2009/06/11 16:52:56
        
        //          
        try {
            //parse()       sdf        ,     
            java.util.Date date6 = sdf.parse("2009/12/10 5:12:02");
            System.out.println(date6.toString()); //  : Thu Dec 10 05:12:02 CST 2009
            
            java.sql.Date date7 = new java.sql.Date(date6.getTime());
            System.out.println(date7.toString()); //  : 2009-12-10
            
            //  : sdf.parse()    java.util.Date  ,     java.sql.Date  
            //java.sql.Date date8 = (java.sql.Date)sdf.parse("2009/12/10 5:12:02"); //   
            
            Timestamp stamp9 = new Timestamp(date7.getTime());
            System.out.println(stamp9.toString()); //  : 2009-12-10 05:12:02.0
        } catch (ParseException e) {
            e.printStackTrace();
        }
        
    }
}