Date/Calendar computations

[David Duran]

Ms. Jennifer Wallace, I hear you on that one...
I'm trying to figure out how to add 1 hour to the current Date for later comparison. But seeing as how a load of functions in the Date class are deprecated and the API points to the Calendar class I'm getting confused.
I simply want to create a Date object and add 1 hour to it. Any ideas? Hahaha, sounds simple

[David Duran]

I came up with this but had to use GregorianCalendar because Calendar is abstract. Anything simpler? I would simply like to bypass that whole Calendar stuff but I don't know if that's possible.
GregorianCalendar cal = new GregorianCalendar();
cal.setTime(new Date());
cal.add(Calendar.HOUR, +1);
Date plusOneHour = cal.getTime();

[Jim Yingst]

Sure:

    Date d = new Date();
    System.out.println(d);
    d.setTime(d.getTime() + (60 * 60 * 1000));
    System.out.println(d);

The GregorianCalendar is useful if you need to work with things like how many days are in a month, or when leap years are, or whether it's Tuesday, etc - but for many simpler things it's easier to just do the calculation yourself in milliseconds.
Note that for some odd, unknown reason, Date is not immutable - even though it's otherwise very much like a wrapper class around a long value representing time in milliseconds. Typically this means you'll want to clone() it or otherwise create a new instance before you return it from a public function - otherwise other programmers can confuse the heck out of you by changing your Date without you realizing it.

[David Duran]

Waaaay easier. Thanks Jim

[Jim Yingst]

For comparison, the Calendar solution:

    Date d = new Date();
    System.out.println(d);
    Calendar cal = new GregorianCalendar();
    cal.setTime(d);
    cal.roll(Calendar.HOUR, 1);
    d = cal.getTime();
    System.out.println(d);

Not that bad - but cetainly longer than it needs to be. On the other hand, if you need something like "noon of the next business day", Calendar's complexities become much more useful.