Due: 5:00pm, Friday, November 21. Value: 30 pts. Submit to Sauron.
The file logins.txt is a log containing information about users who have logged into the 14 laboratory Linux computers between October 1 and November 14, 2008. The file starts as follows.
1222850580 1222855380 1222853220 1222855080 1222854780 1222858560
Each line corresponds to a single user login to a laboratory computer. The first number indicates when the user logged in, measured in seconds since the beginning of 1970. (This is a common way for computers to represent times.) The second number indicates when the user logged out.
Your assignment is to write a Java program that analyzes this log and displays a table listing the amount of time that no computers were in use, that 1 computer was in use, that 2 computers were in use, and so on up to 14 computers. (We would want this information to justify the number of computers in our laboratory.) The following is the output from my solution:
0: 283:36 1: 159:37 : (lines omitted) 13: 0:18 14: 0:00
You should do this by first reading the file into a priority queue
of events, each event representing either a login at a particular
time or a logout at a particular time. Your class to represent
an event needs to implement the
so that when you later remove events from the queue, they are
removed in chronological order.
To create a neatly formatted table for your output, you'll want to use
printf method of
System.out.printf("%2d: %03d\n", 1, 2);
The first string in the parentheses is the format string.
printf method displays each character found in
the format string until it finds a percent sign.
When it sees a percent sign, it uses the characters after
the percent to determine how to display the next parameter that hasn't
been displayed yet.
Here is how it processes the above example.
%2d, indicating to display an integer in decimal (base 10) over two columns; thus, if the integer is below 10, it includes a space before the integer. Since the first parameter after the format string is 1, the string
1is displayed on the screen.
:, which are displayed on the screen as they are.
%03d, which says to display a decimal integer in three columns, padded to the left with zeroes. Since the next parameter after the format string is 2, the string
003is displayed on the screen.
printlninvocations appear on the next line.
The end result is that the line
1: 002 appears on the screen.