Java基础/时间日期格式

Java时间日期格式转换

一、Date转String和String转Date

参考博客：https://www.cnblogs.com/sharpest/p/7879377.html

public static void main(String[] args) {
        String dateStr="2018-2-2 18:00:00";
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date=null;
        try {
            date=formatter.parse(dateStr);
            //字符串转化日期格式=》2018-2-2 18:00:00
            System.out.println("字符串转化日期格式=》"+dateStr);
        } catch (ParseException e) {
            System.out.println("字符串转化日期格式异常=》"+dateStr);
        }
        SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        String strDate=format.format(date);
        //日期转成字符串格式=》2018/02/02 18:00:00
        System.out.println("日期转成字符串格式=》"+strDate);
    }

Calendar日期

一、获取当前日期、当月第1天、当月最后1天

public static void main(String args[]) {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Calendar c = Calendar.getInstance();
        //【1】获取当天
        String curday = format.format(c.getTime());
        System.out.println("===============curDay:" + curday);//2017-12-15
        //【2】获取当前月第一天：
        c.add(Calendar.MONTH, 0);
        //设置为1号,当前日期既为本月第一天
        c.set(Calendar.DAY_OF_MONTH, 1);
        String first = format.format(c.getTime());
        System.out.println("===============first:" + first);//first:2017-12-01
        //【3】获取当前月最后一天
        c.set(Calendar.DAY_OF_MONTH,
                c.getActualMaximum(Calendar.DAY_OF_MONTH));
        String last = format.format(c.getTime());
        System.out.println("===============last:" + last);//last:2017-12-31
        //【4】计算当前日期和第1天的时间差
        Long diff=Long.parseLong(curday.replace("-",""))-Long.parseLong(first.replace("-",""))+1;
        System.out.println("diff:"+diff);//15
    }