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Your task is to write a command-line program that helps to decrypt a message that has been encrypted using a Caesar cipher[1]. Using this method,

Your task is to write a command-line program that helps to decrypt a message that has been encrypted using a Caesar cipher[1]. Using this method, a string may contain letters, numbers, and other ASCII characters, but only the letters (upper- and lower-case) are encrypted a constant number, the shift, is added to the ASCII value of each letter and when letters are shifted beyond z or Z they are wrapped around (e.g. Crazy? becomes Etcba? when shifted by 2).

When your program is correctly run, it will be provided two strings: the encrypted message and a string that is in the deciphered text. If fewer/more arguments are provided, your program is to output an error:

$ java edu.wit.cs.comp1050.PA4a

Please supply correct inputs:

$ java edu.wit.cs.comp1050.PA4a a

Please supply correct inputs:

$ java edu.wit.cs.comp1050.PA4a a b c

Please supply correct inputs:

If the correct arguments are supplied, you are to output any shifts (00-25) that contain the supplied substring:

$ java edu.wit.cs.comp1050.PA4a 'Jvtwbaly zjplujl pz mbu!' is

09: Secfkjuh isyudsu yi vkd!

19: Computer science is fun!

$ java edu.wit.cs.comp1050.PA4a 'Jvtwbaly zjplujl pz mbu!' 'fun!'

19: Computer science is fun!

If no shifts contain the substring, provide an error:

$ java edu.wit.cs.comp1050.PA4a 'Jvtwbaly zjplujl pz mbu!' '?'

No valid shifts found.

To build this program in an object-oriented fashion, you must first implement a Shifter class. This class is constructed with the encrypted string, and then has methods to both shift by an arbitrary amount and find substrings across all shifts.

To implement this class in an efficient manner, you should use a StringBuilder to shift the encrypted string. You might also find it useful to use an ArrayList to accumulate an unknown number of valid shifts. Look to the JavaDocs of the String class for methods to search a string for a substring.

package edu.wit.cs.comp1050;

//TODO: document this class

public class PA4a {

/**

* Error if incorrect command-line arguments are supplied

public static final String ERR_USAGE = "Please supply correct inputs: ";

/**

* Error if shift could not be found

public static final String ERR_NONE = "No valid shifts found.";

/**

* Outputs all shifts of the encrypted string

* that contain the supplied substring

* @param args command-line arguments:

public static void main(String[] args) {

// replace with your code

}

THIS IS THE J UNIT TEST FOR THE PROGRAMME PLEASE CROSS CHECK :

package edu.wit.cs.comp1050.tests;

import java.io.ByteArrayOutputStream;

import java.io.PrintStream;

import java.security.Permission;

import org.junit.Assert;

import edu.wit.cs.comp1050.PA4a;

import edu.wit.cs.comp1050.Shifter;

import junit.framework.TestCase;

public class PA4aTestCase extends TestCase {

private static final String ERR_USAGE = "Please supply correct inputs: ";

private static final String ERR_NONE = "No valid shifts found.";

@SuppressWarnings("serial")

private static class ExitException extends SecurityException {}

private static class NoExitSecurityManager extends SecurityManager

{

@Override

public void checkPermission(Permission perm) {}

@Override

public void checkPermission(Permission perm, Object context) {}

@Override

public void checkExit(int status) { super.checkExit(status); throw new ExitException(); }

}

@Override

protected void setUp() throws Exception

{

super.setUp();

System.setSecurityManager(new NoExitSecurityManager());

}

@Override

protected void tearDown() throws Exception

{

System.setSecurityManager(null);

super.tearDown();

}

private void _test(String[] a, String msg) {

final ByteArrayOutputStream outContent = new ByteArrayOutputStream();

final String expected = TestSuite.stringOutput(new String[] {

msg + "%n"

}, new Object[] {});

System.setIn(null);

System.setOut(new PrintStream(outContent));

try {

PA4a.main(a);

} catch (ExitException e) {}

assertEquals(expected, outContent.toString());

System.setIn(null);

System.setOut(null);

}

private void _testShift(String s, int[] n, String[] eShift) {

Shifter shifter;

shifter = null;

try {

shifter = new Shifter(s);

} catch (ExitException ex) {}

assertNotNull(shifter);

for (int i=0; i

String result = null;

try {

result = shifter.shift(n[i]);

} catch (ExitException ex) {}

assertNotNull(result);

assertEquals(String.format("\"%s\".shift(%d)", s, n[i]), eShift[i], result);

}

private void _testFindShift(String s, String sub, int[] e) {

Shifter shifter = null;

int[] result = null;

try {

shifter = new Shifter(s);

} catch (ExitException ex) {}

assertNotNull(shifter);

try {

result = shifter.findShift(sub);

} catch (ExitException ex) {}

assertNotNull(result);

Assert.assertArrayEquals(e, result);

}

public void testShift() {

_testShift("",