java-Math、Random、Date、Calenda…

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import java.util.*;
import java.text.*;
class DateDemo
{
public static void main(String[] args)
{
  //Date、Format、SimpleFormat.
  Date d = new Date();
  String str = "yyyy年MM月dd日hh:mm:ss aa";
  SimpleDateFormat sdf = newSimpleDateFormat(str);
  String s = sdf.format(d);
  System.out.println(s);

  //Calender.
  //Calendar c =Calendar.getInstance();
  //System.out.println(c.get(Calendar.YEAR)+"年"+(c.get(Calendar.MONTH)+1)+"月"+c.get(Calendar.DAY_OF_MONTH)+"日");
  getDay(2012);

//Math.random() 随机数
getRandom();
}

//某一年的二月有多少天.
public static void getDay(int year)
{
  Calendar c =Calendar.getInstance();
  c.set(year, 2, 1);//月份从0开始计数
  c.add(Calendar.DAY_OF_MONTH,-1);
  //System.out.println(c.get(Calendar.YEAR)+"年"+(c.get(Calendar.MONTH)+1)+"月"+c.get(Calendar.DAY_OF_MONTH)+"日");
  System.out.println(c.get(Calendar.DAY_OF_MONTH));
}

//取10以内的10个随机数
public static void getRandom()
{
  Random r = new Random();
  for (int x = 0; x< 10; x++)
  {
   //方法一：Math.random()
   //double d =Math.random()*10+1;
   //System.out.println((int)d);
   //方法二：Random类

   int a =r.nextInt(10);
   System.out.println(a);
  }
}
}