在不使用库的情况下遍历日期范围-Java

Question

Hi I want to iterate through a date range without using any libraries. I want to start on 18/01/2005(want to format it to yyyy/M/d) and iterate in day intervals until the current date. I have formatted the start date, but I dont know how I can add it to a calendar object and iterate. I was wondering if anyone can help. Thanks

String newstr = "2005/01/18";
SimpleDateFormat format1 = new SimpleDateFormat("yyyy/M/d");

Answer 1

Date date = format1.parse(newstr);
Calendar calendar = new GregorianCalendar();
calendar.setTime(date);
while (someCondition(calendar)) {
    doSomethingWithTheCalendar(calendar);
    calendar.add(Calendar.DATE, 1);
}

Answer 2

Use SimpleDateFormat to parse a string into a Date object or format a Date object into a string.

Use class Calendar for date arithmetic. It has an add method to advance the calendar, for example with a day.

See the API documentation of the classes mentioned above.

Alternatively, use the Joda Time library, which makes these things easier. (The Date and Calendar classes in the standard Java API have a number of design issues and are not as powerful as Joda Time).

Answer 3

Java, and in fact many systems, store time as the number of Milliseconds since 12:00am january first 1970 UTC. this number can be defined as a long.

//to get the current date/time as a long use
long time = System.currentTimeMillis();

//then you can create a an instance of the date class from this time.
Date dateInstance = new Date(time);

//you can then use your date format object to format the date however you want.
System.out.println(format1.format(dateInstance));

//to increase by a day, notice 1000 ms = 1 second, 60 seconds = 1 minute,
//60 minutes = 1 hour 24 hours = 1 day so add 1000*60*60*24 
//to the long value representing time.
time += 1000*60*60*24;

//now create a new Date instance for this new time value
Date futureDateInstance = new Date(time);

//and print out the newly incremented day
System.out.println(format1.format(futureDateInstance));