Question

If I have a vector containing a number of unsorted files, how can I categorize them by their last modified date?

what I need to do is to place the files into 3 other vectors, with the last modified date of “Today”, “Yesterday”, and “This Week”.

Vector<File> files;  //This vector contains all the files that need to be categorized
Vector<File> todayFiles;  //Empty
Vector<File> yesterdayFiles;  //Empty
Vector<File> weekFiles;  //Empty

I know I can use file.lastModified() to get the date, but it returns the date in milliseconds formatted as a long int, so I am not sure if there is an easier way to compare and group the dates without doing some intricate arithmetic work.

I am new to Java, so I have no idea how to approach this question, any help would be appreciated.

UPDATE

I was able to get the code to work somehow, but it is still not working properly. This is what I have:

private Calendar cal;
private long todayTime;

this.cal = Calendar.getInstance();
this.cal.set(Calendar.HOUR_OF_DAY, 0);
this.cal.set(Calendar.HOUR, 0);
this.cal.set(Calendar.MINUTE, 0);
this.cal.set(Calendar.SECOND, 0);
this.cal.set(Calendar.MILLISECOND, 0);
this.todayTime = cal.getTimeInMillis();

Now when I try to add them into the vector that I created, it is only grabbing files that have been modified in the PM of today’s date:

for(int i = 0; i < this.files.size(); i++) {
    if(this.files.get(i).lastModified() >= this.todayTime) {
        this.today.add(this.files.get(i));  
    }
}

Is there anything that I am doing wrong? Thank you for all the great responses by the way!

Answer 1

You can use the Calendar class to get timestamps for the required dates such as today and yesterday. For example, to get today’s (midnight) timestamp:

Calendar cal = Calendar.getInstance();
// cal initially contains current time
cal.set(Calendar.HOUR, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);

long todayTimestamp = cal.getTimeInMillis();

Then you can compare this timestamp with file.lastModified() and put the file into the corresponding vector.