随机验证码，截取字符串，时间的读写

验证码

String a=new String("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789");
  String yzm="";
  for(int i=0;i<4;i++){
   int sj=(int)(Math.random()*1000);
   int b =sj%a.length();
      yzm +=a.substring(b, b+1);
  }
  System.out.println(yzm);

截取字符串

 String a=new String("<student><name>张三</name><sex>男</sex><class>1116班</class></student>");
  String a1=a.replaceAll("<student>", "").replaceAll("</student>", "");
  int name=a1.lastIndexOf("<name>");
  int name1=a1.indexOf("</name>");
  int sex=a1.lastIndexOf("<sex>");
  int sex1=a1.indexOf("</sex>");
  int i =a1.lastIndexOf("<class>");
  int j =a1.indexOf("</class>");
  String xingming=a1.substring(name+6, name1);
  String xingbie=a1.substring(sex+5,sex1);
  String banji=a1.substring(i+7,j);
  
  System.out.println("姓名："+xingming+" "+"性别："+xingbie+" "+"班级："+banji);

时间的读写操作

Calendar a=Calendar.getInstance();
  int year =2016;
  int month=8;
  int date=12;
  a.set(year, month,date);    //赋值
  SimpleDateFormat b=new SimpleDateFormat("yyyy-MM-dd");     //定义一个格式化工具
  String c=b.format(a.getTime());                //格式化
  System.out.println(c);