Check if 24 hours have passed (reading from a string)

Question

I am saving date\'s in a file in the following format as a string.

Sat Jul 21 23:31:55 EDT 2012

How can I check if 24 hours have passed? I am a

Answer 1

You can do something like this:

try {

    // reading text...
    Scanner scan = new Scanner( new FileInputStream( new File( "path to your file here..." ) ) );
    String dateString = scan.nextLine();

    // creating a formatter.
    // to understand the format, take a look here: http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
    // EEE: Day name of week with 3 chars
    // MMM: Month name of the year with 3 chars
    // dd: day of month with 2 chars
    // HH: hour of the day (0 to 23) with 2 chars
    // mm: minute of the hour with 2 chars
    // ss: second of the minute with 2 chars
    // zzz: Timezone with 3 chars
    // yyyy: year with 4 chars
    DateFormat df = new SimpleDateFormat( "EEE MMM dd HH:mm:ss zzz yyyy", Locale.US );

    // parsing the date (using the format above, that matches with your date string)
    Date date = df.parse( dateString );

    // now!
    Date now = new Date();

    // gets the differente between the parsed date and the now date in milliseconds
    long diffInMilliseconds = now.getTime() - date.getTime();

    if ( diffInMilliseconds < 0 ) {
        System.out.println( "the date that was read is in the future!" );
    } else {

        // calculating the difference in hours
        // one hour have: 60 minutes or 3600 seconds or 3600000 milliseconds
        double diffInHours = diffInMilliseconds / 3600000D;
        System.out.printf( "%.2f hours have passed!", diffInHours );

    }

} catch ( FileNotFoundException | ParseException exc ) {
    exc.printStackTrace();
}