JAVA日期格式转换与数据类型转换

看了网上各种资料，感觉很庞杂，自己总结出一些比较简练得代码，以备日后需要直接获取。

日期格式转换

import java.util.Date;import java.text.ParseException;import java.text.SimpleDateFormat;     public static void main (String[] args) throws ParseException     {        String start_time="2017-08-01 00:00:00";        String end_time="2017-08-01 14:32:00";        //设置日期格式        //SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");//12小时制           SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");        //当前系统日期        Date Now = new Date();         String now_time = df.format( Now );         //日期转换为数据        java.util.Date end = df.parse(end_time);             java.util.Date begin=df.parse(start_time);         java.util.Date now=df.parse(now_time);        //日期比较大小        long a=now.getTime()-begin.getTime();        long b=end.getTime()-now.getTime();        long c=end.getTime()-begin.getTime();    }

日期间隔天数

import java.util.Calendar;public static void main (String[] args) throws ParseException     {    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");         //日期间隔天数        Calendar cal = Calendar.getInstance();            long time3 = 0;        long time4 = 0;            {             cal.setTime(df.parse(time1));                time3 = cal.getTimeInMillis();                 cal.setTime(df.parse(time2));              time4 = cal.getTimeInMillis();              }            catch(Exception e)            {             e.printStackTrace();            }        long time_interval=(time4-time3)/(1000*3600*24);          return Integer.parseInt(String.valueOf(time_interval));         }

时间差

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");   java.util.Date now = df.parse("2017-08-03 13:31:40");   java.util.Date date=df.parse("2017-08-02 11:30:24");   long l=now.getTime()-date.getTime();   long day=l/(24*60*60*1000);   long hour=(l/(60*60*1000)-day*24);   long min=((l/(60*1000))-day*24*60-hour*60);   long s=(l/1000-day*24*60*60-hour*60*60-min*60);   System.out.println(""+day+"天"+hour+"小时"+min+"分"+s+"秒");

SimpleDateFormat dfs = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");   java.util.Date begin=dfs.parse("2004-01-02 11:30:24");   java.util.Date end = dfs.parse("2004-03-26 13:31:40");   long between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒   long day1=between/(24*3600);   long hour1=between%(24*3600)/3600;   long minute1=between%3600/60;   long second1=between%60/60;   System.out.println(""+day1+"天"+hour1+"小时"+minute1+"分"+second1+"秒");

字符转换

String->Double

double a = Double.parseDouble(A);

Double->String

 String A=nf.format(a);

String->Int

String str = "123";try {    int a = Integer.parseInt(str);} catch (NumberFormatException e) {    e.printStackTrace();}

int a = Integer.parseInt(A);int a = Integer.valueOf(A).intValue();

Int->String

String A = String.valueOf(a);String A = Integer.toString(a);

四舍五入

NumberFormat nf = NumberFormat.getInstance();        nf.setRoundingMode(RoundingMode.HALF_UP);        //设置最小保留几位小数        nf.setMinimumFractionDigits(2);        //设置最大保留几位小数        nf.setMaximumFractionDigits(2);        String Price=nf.format(p);