Check if current time is more than an hour from "last_updated" time

Question

On my Android App, I'd like to only re-import my data if it's been at least X hours since the last import.

I'm storing the last_updated time in my sqlite database in this format: 2012/07/18 00:01:40

How can I get "hours from then" or something like that?

My code thus far:

package com.sltrib.utilities;

import java.text.SimpleDateFormat;
import java.util.Calendar;

public class DateHelper
{

  public static String now()
  {
      Calendar currentDate = Calendar.getInstance();
      SimpleDateFormat formatter = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
      String dateNow = formatter.format(currentDate.getTime());
      //System.out.println("Now the date is :=>  " + dateNow);
      return dateNow;
  }

  public static int hoursAgo(String datetime)
  {
      //return the number of hours it's been since the given time
      //int hours = ??
      //return hours;
  }

}

Solution

You're going to want to do math between two Calendars or Dates.

Note: Aspects of Date are deprecated, see below for Calendar!

Here's an example using Date:

public static int hoursAgo(String datetime) {
    Date date = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.ENGLISH).parse(datetime); // Parse into Date object
    Date now = Calendar.getInstance().getTime(); // Get time now
    long differenceInMillis = now.getTime() - date.getTime();
    long differenceInHours = (differenceInMillis) / 1000L / 60L / 60L; // Divide by millis/sec, secs/min, mins/hr
    return (int)differenceInHours;
}

There are some try/catch blocks involved here (which you should probably handle with throws), but this is the basic idea.

Edit: Since parts of Date are deprecated, here is the same method using Calendar:

public static int hoursAgo(String datetime) {
    Calendar date = Calendar.getInstance();
    date.setTime(new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.ENGLISH).parse(datetime)); // Parse into Date object
    Calendar now = Calendar.getInstance(); // Get time now
    long differenceInMillis = now.getTimeInMillis() - date.getTimeInMillis();
    long differenceInHours = (differenceInMillis) / 1000L / 60L / 60L; // Divide by millis/sec, secs/min, mins/hr
    return (int)differenceInHours;
}