Java 常用到的日期問題

1.日期 = 上週 下週
2.日期 = 前一天 後一天
3.日期 = 相差天數
-------------------------上週 下週------------------------------------------
package com;

import java.text.SimpleDateFormat;

import java.util.Calendar;

public class Test01 {

    public static void main(String args[]){

        int i=0;

          Calendar cal = Calendar.getInstance();

          Calendar cal1 = Calendar.getInstance();

          int n = i;

          String monday;

          cal.add(Calendar.DATE, n*7);

          monday = new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime());


          int n1 = i-1;

          String monday1;

          cal1.add(Calendar.DATE, n1*7);

          monday1 = new SimpleDateFormat("yyyy-MM-dd").format(cal1.getTime());

          System.out.println(monday1+"  :  "+monday);

    }

}


-------------------------前一天 後一天-----------------------------------

package com;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
public class Test02 {
    public static void main(String[] args) throws ParseException {  
         
                String Date_Text ="2013-03-31";
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");  
     
                Calendar cal = Calendar.getInstance();  
                cal.setTime(sdf.parse(Date_Text));  
                cal.add(Calendar.DATE, -1);//減一天  
              //cal.add(Calendar.MONTH, n);//增加一个月  
     
                System.out.println(" 增加一天 : "+ sdf.format(cal.getTime()));  
     
           
    }
}
--------------------------相差天數-----------------------------------
package com;
import java.util.Date;

public class Test03 {
    public static void main(String[] args) {
          String s1 = "2013-04-01";
          String s2 = "2013-03-27";
          String t1 = s1.replace('-','/');
          String t2 = s2.replace('-','/');
          try{
              Date dt1= new Date(t1);
              Date dt2= new Date(t2);
              System.out.println("dt1="+dt1.getTime());
              System.out.println("dt2="+dt2.getTime());
              long l = dt1.getTime() - dt2.getTime();   
              System.out.println(l);
              System.out.println("相差天數 "+l/60/60/1000/24);
            }catch(Exception e){
                System.out.println("exception"+e.toString());
            }
    }
}