1: import java.util.*;

   2: class SystemDemo 

   3: {

   4:     public static void main(String[] args) 

   5:     {

   6:         Properties prop = System.getProperties();

   7:  

   8:         //设置系统的自定义信息

   9:         //System.setProperty("mykey","myvalue");

  10:  

  11:         //获取指定属性

  12:         String name = System.getProperty("os.name");

  13:  

  14:         System.out.println("os name = "+name);

  15:  

  16:         //Properties是Hashtable

  17:         for(Object obj : prop.keySet())

  18:         {

  19:             String value = (String)prop.get(obj);

  20:             System.out.println(obj+"::"+value);

  21:         }

  22:         

  23:     }

  24: }

   1: class RuntimeDemo 

   2: {

   3:     public static void main(String[] args) throws Exception

   4:     {

   5:         //获取runtime对象

   6:         Runtime r = Runtime.getRuntime();

   7:         

   8:         //执行打开记事本命令,该程序的检索目录来自于path环境变量

   9:         Process p = r.exec("notepad.exe");

  10:  

  11:         Thread.sleep(4000);

  12:         

  13:         //结束记事本进程

  14:         p.destroy();

  15:  

  16:         //执行notepad，并用notepad打开一个文件

  17:         Process p1 = r.exec("notepad.exe d:\\code\\java_interview\\Test17.java");

  18:         

  19:  

  20:     }

  21: }

   1: import java.util.*;

   2: import java.text.*;

   3:  

   4: class DateDemo 

   5: {

   6:     public static void main(String[] args) 

   7:     {

   8:         //获取时间对象

   9:         Date d = new Date();

  10:         //打印未格式化的时间

  11:         System.out.println(d);

  12:         

  13:         //设置格式为 "2013-10-23 星期三 11:15:15"

  14:         SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-dd E HH:mm:ss");

  15:  

  16:         //格式化时间对象，得到格式化后的时间

  17:         String time = sdf.format(d);

  18:         

  19:         //打印时间

  20:         System.out.println(time);

  21:     }

  22: }

   1: import java.util.*;

   2:  

   3:  

   4: class CalendarDemo 

   5: {

   6:     public static void main(String[] args) 

   7:     {

   8:         Calendar c = Calendar.getInstance();

   9:     

  10:         showTime(getYestTime());

  11:  

  12:         //System.out.println(getFebDays(2011));

  13:     }

  14:  

  15:     //获取随机年的二月有几天

  16:     private static int getFebDays(int year)

  17:     {

  18:         Calendar c = Calendar.getInstance();

  19:         

  20:         //设置时间为某年的3月1日

  21:         c.set(year,2,1);

  22:         //天数减一，得到2月最后一天

  23:         c.add(Calendar.DAY_OF_MONTH,-1);

  24:         //返回2月的最后一天

  25:         return c.get(Calendar.DAY_OF_MONTH);

  26:     }

  27:  

  28:     //获取昨天现在这个时刻

  29:     private static Calendar getYestTime()

  30:     {

  31:         Calendar c = Calendar.getInstance();

  32:         

  33:         //天数减一

  34:         c.add(Calendar.DAY_OF_MONTH,-1);

  35:  

  36:         return c;

  37:  

  38:     }

  39:  

  40:     //打印时间

  41:     private static void showTime(Calendar c)

  42:     {

  43:         //月份编码表

  44:         String[] mons = {"一月","二月","三月","四月","五月","六月","七月","八月","九月","十月","十一月","十二月"};

  45:         //星期编码表

  46:         String[] days = {"","星期日","星期一","星期二","星期三","星期四","星期五","星期六"};

  47:         

  48:         //获取对应月份和星期的角标

  49:         int mon_index = c.get(Calendar.MONTH);

  50:         int day_index = c.get(Calendar.DAY_OF_WEEK);

  51:  

  52:         //打印时间

  53:         System.out.println(c.get(Calendar.YEAR)+"年"

  54:                             +mons[mon_index]+

  55:                             +c.get(Calendar.DAY_OF_MONTH)+"日 "

  56:                             +days[day_index]+" "

  57:                             +c.get(Calendar.HOUR_OF_DAY)+":"

  58:                             +c.get(Calendar.MINUTE));

  59:     }

  60: }