Java 日期计算 | 易学教程

Java 计算日期加、减一天

方法一

SimpleDateFormat newdate = new SimpleDateFormat("HH:mm:ss");//设置时间格式
            String time1 =  newdate.format(new Date());//获取当前系统时间
            String time2= "00:00:00";//大于时间
            String time3= "15:59:59";//小于时间
            Date dt1 = newdate.parse(time1);
            Date dt2 = newdate.parse(time2);
            Date dt3 = newdate.parse(time3);
            if(dt2.getTime() < dt1.getTime() || dt1.getTime() <dt3.getTime()) {
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
                Date date = new Date();
                Calendar rightNow = Calendar.getInstance();
                rightNow.add(Calendar.DATE,-2);//当前时间减2天
                Date dt8 = rightNow.getTime();
                newRQ = sdf.format(dt8);
            }else {
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
                Date date = new Date();
                Calendar rightNow = Calendar.getInstance(); 
                rightNow.add(Calendar.DATE,-1);//当前时间减1天
                Date dt8 = rightNow.getTime();
                newRQ = sdf.format(dt8);
            }

方法二

Date date = new Date();//获取当前时间    
Calendar calendar = Calendar.getInstance();    
calendar.setTime(date);    
calendar.add(Calendar.YEAR, -1);//当前时间减去一年，即一年前的时间    
calendar.add(Calendar.MONTH, -1);//当前时间前去一个月，即一个月前的时间    
calendar.getTime();//获取一年前的时间，或者一个月前的时间

日期比较

两个string类型的日期比较大小

public static int compare_date(String DATE1, String DATE2) {
         DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
         try {
             Date dt1 = df.parse(DATE1);
             Date dt2 = df.parse(DATE2);
             if (dt1.getTime() > dt2.getTime()) {
                 System.out.println("dt1 在dt2前");
                 return 1;
             } else if (dt1.getTime() < dt2.getTime()) {
                 System.out.println("dt1在dt2后");
                 return -1;
             } else {
                 return 0;
             }
         } catch (Exception exception) {
             exception.printStackTrace();
         }
         return 0;
     }

返回两个string类型日期之间相差的天数

public static int daysBetween(String smdate,String bdate){  
         SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");  
         Calendar cal = Calendar.getInstance();    
         long time1 = 0;
         long time2 = 0;
         
         try{
              cal.setTime(sdf.parse(smdate));   
              time1 = cal.getTimeInMillis();    
              cal.setTime(sdf.parse(bdate)); 
              time2 = cal.getTimeInMillis();  
         }catch(Exception e){
             e.printStackTrace();
         }
         long between_days=(time2-time1)/(1000*3600*24);  
             
        return Integer.parseInt(String.valueOf(between_days));     
     }

返回两个string类型日期相差的小时数

public static int daysBetween2(String startTime, String endTime) {
          SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH");  
          Calendar cal = Calendar.getInstance();    
          long time1 = 0;
          long time2 = 0;
          
          try{
               cal.setTime(sdf.parse(startTime));   
               time1 = cal.getTimeInMillis();    
               cal.setTime(sdf.parse(endTime)); 
               time2 = cal.getTimeInMillis();  
          }catch(Exception e){
              e.printStackTrace();
          }
          long between_days=(time2-time1)/(1000*3600);  
              
         return Integer.parseInt(String.valueOf(between_days));     
      }

来源：https://www.cnblogs.com/xianyao/p/11006085.html

标签

date

simpledateformat

string