Java program that will read dates from an external text file and identify which two dates in the file have the fewest number of

days between them and which two dates have the largest number of days between them and output those

pairs of dates and the number of days between each pair.

For this program, you will be provided with a

Date

class that you will use to store and process dates with so

that you don't have to manage that information manually. This should enable you to focus on the logic of the

program itself rather than adding in details of storing and processing the dates.

NOTE

: See later in the assignment for details on how the output should be formatted.

For this program, you will also need to implement at least two additional methods other than

main()

.

These

methods can accomplish whatever task you want them to, such as: read the file of dates, sort an array of

dates, display the list of dates, find the smallest range between two dates, find the largest range of dates

between two dates, etc.

The methods you write will need to have complete Javadoc documentation and be used (called) at least once

each during your program's execution.

It is acceptable to write more than two additional methods if you would like in order to practice breaking

programs into smaller, more manageable units of code.

Program 12 - Spring 2018

Overview of Program

Writing two methods on your own

The file that you will read dates from will look like this:

5

1/1/1900

1/2/1900

12/5/1798

7/4/3001

8/1/2028

The first value of the file will be an

int

value indicating how many dates will be present in the file.

The value

could be any value from

2

and up.

Each file will be guaranteed to have at least two dates in it.

Each date in the file will be on a line by itself and will be in the format of

MM/DD/YYYY

, where

MM

is the

month,

DD

is the day, and

YYYY

is the year. Information about easily processing dates in this format is

discussed later in this document.

For this program, all dates in a file will be valid dates, but functionality is provided within the

Date

class to

identify invalid dates and handle them appropriately.

There may be duplicate entries for the same date in the file.

Dates can be in the range

1/1/1753

to

12/31/3000

.

In order to process a file for input instead of keyboard input, you'll need to be able to open and read from a

separate text file in Java.

There are a number of different ways to do this, and you'll explore more involved

ways to process files if you take more programming courses, but for what we need this semester we'll create a

Scanner

that is attached to a file so that input will basically behave the same way that you've been

processing things all semester, just from a file instead of the keyboard.

To practice with this idea, first create a file named

test.txt

in the same directory that your program file will

reside in that looks like this:

Format of the file

Reading input from a file instead of the keyboard

5

51

2112

42

12

-123

Now edit a file called

TestingFileInput.java

in jGRASP and place the following code into it.

Compile

and run the code to see what it does.

Pay close attention to the

throws FileNotFoundException

code

added to the header of the

main()

method, which is new and only necessary right now when processing

external files:

import

java

.

util

.

Scanner

;

import

java

.

io

.

File

;

Import java

.

io

.

FileNotFoundException

;

public

class

TestingFileInput

{

public

static

void

main

(

String args

[

]

)

throws

FileNotFoundException

{

// Create a regular Scanner for keyboard input

Scanner keyboard

=

new

Scanner

(

System

.

in

)

;

// Now create a String variable and read the filename

System

.

out

.

println

(

"Enter input filename: "

)

;

String inFile

;

// Notice the use of the System.in Scanner for this input

inFile

=

keyboard

.

next

(

)

;

// Need to create a File variable based on the inFile file name

File file

=

new

File

(

inFile

)

;

// Now create a Scanner attached to the file instead of System.in

// This Scanner will be used for file input!!!

Scanner fileInput

=

new

Scanner

(

file

)

;

// Read something out of the file, which is an integer

int

v1

=

fileInput

.

nextInt

(

)

;

System

.

out

.

println

(

"First int of the file is : "

+

v1

)

;

// Set up a loop that reads the rest of the int data from the file

System

.

out

.

println

(

"Now reading the rest of the data!"

)

;

for

(

int

which

=

0

;

which

<

v1

;

which

++

)

{

int

v

=

fileInput

.

nextInt

(

)

;

System

.

out

.

printf

(

"A value from the file: %d "

,

v

)

;

}

}

}

Java

Your program may not compile with an error that looks like this:

FileInput.java:18: error: unreported exception FileNotFoundException;

must be caught or declared to be thrown

Scanner fileInput = new Scanner(file);

If this happens, make sure you go back and add in the

throws FileNotFoundException

code on the

main()

method header line.

This should take care of that situation.

You should notice that the example program creates two different

Scanner

variables.

Variable

keyboard

is used to read the filename from the keyboard, as we've been doing all semester so far.

Variable

fileInput

is connected to an external file to pull data from.

When you run the code and are prompted for a file name, enter

test.txt

or whatever you called the file

you created. If the file exists, the program should read the data from that file and output it to the screen.

Notice what happens when you enter a filename that doesn't exist; the program should exit with some sort of

error like this:

Exception in thread "main" java.io.FileNotFoundException: test.data

(No such file or directory)

at java.base/java.io.FileInputStream.open0(Native Method)

at java.base/java.io.FileInputStream.open(FileInputStream.java:196)

at java.base/java.io.FileInputStream.(FileInputStream.java:139)

at java.base/java.util.Scanner.(Scanner.java:611)

at FileInput.main(FileInput.java:18)

It is important and imperative that you work with this code until you are certain you have a good handle

on how it's setting up an external file for reading before moving on to the next part of the assignment.

The code doesn't compile with a really weird error!

The program uses multiple

Scanner

variables! What?

Okay, it compiles and runs ... what now?

A

Date

object can store a date between

1/1/1753

and

12/31/3000

.

Objects of

Date

class have the following public methods available for you to use.

Please note that

you do not need to write these methods; they are available for you to use in the

Date

class

that is provided in the

Date.class

file you will download.

You don't need to use any

import

statements or anything fancy to use the

Date

class. Just create a new

Date

object in your program using the constructor as described below and you can move forward from

there.

Method

Description and Example

Date()

Default constructor, used to create a new

Date

object. The

date is set to 1/1/1753.

Date d1 = new Date();

Date(int m, int d, int y)

Specific constructor, used to create a new

Date

object with

a given date.

Date d2 = new Date(11,27,2017);

setDate(int m, int d, int y)

Attempts to set the date to the given month

m

, day

d

,

and year

y

. Returns

true

if the date was valid.

Returns

false

and sets the date to 1/1/1753 if the attempted date

was invalid.

d1.setDate(4,1,2018);

daysSince1753()

Returns an

int

value denoting how many days since

1/1/1753 the object's date is.

int w = d2.daysSince1753();

toString()

Allows printing of the object's date.

System.out.print(d2);

What can objects of the

Date

class do?

The closest dates will be determined by comparing each date to all of the dates in the file except for itself.

The

result may be

0

, but only if there are duplicate dates in the file.

The furthest dates will also be determined by comparing each date to all of the dates in the file except itself.

Given the storage range of dates possible in a

Date

object, the maximum number of days between dates

could be

455821

.

See the sample runs at the end of the file for examples of different results.

For previous assignments when entering dates, the month, day, and year needed to be entered separately.

For

this assignment, you'll change a property of the

Scanner

attached to the file that you create so that you can

read dates in

MM/DD/YYYY

format.

By default, a

Scanner

uses whitespace like spaces and newlines (enter/return) to identify different pieces of

input, like this:

Scanner get

=

new

Scanner

(

System

.

in

)

;

System

.

out

.

print

(

"Enter your date: "

)

;

int

m

=

get

.

nextInt

(

)

;

int

d

=

get

.

nextInt

(

)

;

int

y

=

get

.

nextInt

(

)

;

Determining Closest and Furthest Dates

Closest Dates

Furthest Dates

Examples

Considerations for Entering and Validating Dates

Entering Dates

Java

Input to this code could be entered like this:

Enter your date: 4

16

2018

or like this:

Enter your date: 4 16 2018

Either way, variable

m

would get a value of

4

, variable

d

would get a value of

16

and variable

y

would get a value of

2018

.

In order to enter dates in MM/DD/YYYY format, using slashes, the

Scanner

attached to your file needs to

behave differently. The easiest way to do this is to change the way the

Scanner

reads values from the

keyboard.

As mentioned in the last section, a

Scanner

uses whitespace as a delimiter between input by

default.

To change this behavior, you can use the

useDelimiter()

method from the

Scanner

class.

More information about the

useDelimiter()

method can be found at

http://bit.ly/scannerdelimiter

.

To enable a

Scanner

to use, for instance, slashes

/

as delimiters in addition to spaces, you can use the

following code in your program:

Scanner get

=

new

Scanner

(

System

.

in

)

;

get

.

useDelimiter

(

"[/\\s+]+"

)

;

// notice two backslashes here!

System

.

out

.

print

(

"Enter your date: "

)

;

int

m

=

get

.

nextInt

(

)

;

int

d

=

get

.

nextInt

(

)

;

int

y

=

get

.

nextInt

(

)

;

Now, dates can be entered in any of the following four ways:

Enter your date: 4

16

2018

Changing

Scanner

behavior

Java

or

Enter your date: 4 16 2018

or

Enter your date: 4/16/2018

or

Enter your date: 4 / 16 / 2018

The

useDelimiter()

method changes the behavior of the

Scanner

by providing a list of items that can

be seen as delimiters between pieces of information.

[/\\s+]+

tells Java that it can use either a forward

slash

/

or a whitespace character

\s

(such as space, return, etc) to identify different inputs.

The key to having this work with input from a text file is to apply the

.useDelimiter()

method to the

Scanner

you would like to change the behavior of. So, if you have a

Scanner

attached to a file, then you

want to use the

.useDelimiter()

method on that

Scanner

.

The output of your program should look like the following sample:

Enter filename to process: d1.txt

The sorted dates from the file are:

1: 11/30/1955

2: 11/23/2015

3: 11/24/2015

4: 11/25/2015

5: 11/26/2015

6: 11/28/2015

7: 11/29/2015

8: 11/30/2015

9: 12/02/2015

10: 02/23/2016

Closest (1): 11/23/2015 and 11/24/2015

Furthest (22000): 11/30/1955 and 02/23/2016

Make sure to include the following items in the format seen above:

The program should output a list of the dates themselves, one per line, sorted from earliest date to latest

date.

Then output the dates that are "closest" to each other, including the number of days between the two

dates, in "sorted" order with the earlier date listed first.

Finally, output the dates that are the "furthest" from each other, including the number of days between the

two dates, in sorted order with the earlier date listed first.

The starter code can be found below:

import java.util.Scanner; import java.io.File; import java.io.FileNotFoundException;

public class FileOfDates { /** * It's the main method! * @param args Arguments to the main method * @throws Exception is a file-related exception we're not processing */

public static void main(String args[]) throws FileNotFoundException { // The Scanner named get is for keyboard input Scanner get = new Scanner(System.in); System.out.print("Enter filename to process: "); String fn = get.next();

// The File thing attempts to connect to a file named in variable fn File thing = new File(fn); // The Scanner named fileInput is for reading data from the user Scanner fileInput = new Scanner(thing); // The following statement changes default behavior of this file // Scanner; see assignment for more information fileInput.useDelimiter("[/\\s]+");