Code Quality Tests

1. Main: Main class is named Crypt in the default package (source Crypt.java).
2. Modularity: Source code uses separate classes for main (Crypt.java), Shift cipher, and Unicode cipher. Partial credit for dividing code into Encrypt.java and Decrypt.java. No point for all code in one class, or putting the Cipher code in the main class (Crypt.java).
3. No Big String: Code does not try to read entire file into a String, a List of Strings, or StringBuilder! It should read one block (array) or one line, encrypts it, and write the result.
4. No String Cat: Code does not use string concatenation for building up cipher text or plain text. No string += string or string += char.

   //WRONG
   String ciphertext = "";
   for(int k=0; k<text.length(); k++) {
       char c = text.charAt(k);   // this is bad, too
       c = /* enncrypt char */;
       ciphertext += c;           // WRONG - string concatenation
   }

5. CLI Validates Input: Crypt prints errors if command line arguments are missing or invalid. Examples:
   • Crypt -alg print error for missing algorithm name (not throw ArrayIndexOutOfBounds exception)
   • Crypt -mode icecream print error for invalid mode
   • Crypt -in doesntexist print error that input file doesn't exist
   • Crypt -foo print error for invalid option -foo
   • Crypt -key five OK to throw NumberFormatException, but error message is better.

Test Files

File name	Contents
data	source for Crypt -data "text" test
file1	spaces and newlines
file2	letters and standard symbols
file3	Thai text on two lines, one English word
file4	256K English text

Test Script

The file testcrypt is a Bash script that will compile the student's code and run tests.

First you need to edit two variables:

TESTDIR= directory where the test files (file1, file2, ...) are located
OUTDIR= directory for creating output from student code, such as /tmp

To run:

# chdir to where their source code is
cd student/pa2/src  
# run the script. You may need to specify path, too.
testcrypt

If the student "main" class is named CryptApp.java instead of "Crypt.java", then specify the class name:

testcrypt CryptApp

Test Cases and Expected Results

For each test case below, the script runs the test in the table and directs the output to a file (-out somefile).
Then compare the output file to a reference file (expected result).

java Crypt -in file2 -alg shift -key 10 -out file2.enc
# compare output to a reference file (file2.shift10)
cmp file2.enc  file2.shift10

The tests involving file4 are different: encrypt file4 using the command line args, then decrypt the output file, and compare the the decrypted file to the original file. They should be exactly the same.

for example:

java Crypt -alg unicode -key 4999 -mode enc -in file4 -out file4.enc 
java Crypt -alg unicode -key 4999 -mode dec -in file4.enc -out file4.dec 
# use the linux "cmp" program to compare result to the original file
cmp file4 file4.dec

In tests of file4, if the program runs for more then 1 second then it counts as failure. A long run time means the code is concatenating many Strings, which it should not do.

If encrypt/decrypt of file4 fails, please look at the output from cmp. The file is 262,700 bytes long. If cmp reports:

differ at byte 262,700
// or
cmp: EOF file4 after byte 262,700

then their code is almost correct but it corrupting the last char or writing an extra char. Anusid's code is like this.

I didn't show the -out filename in the table below. You can use any output filename.

Test	Arguments to Crypt	Output should be same as
1	-in file1 -alg shift -key 10	file1
2	-in file2 -alg shift	file2
3	-in file2 -alg shift -key 10	file2.shift10
4	-in file2 -alg shift -key 100	file2.shift100
5	-data "$data" -alg shift -key 13	data.shift13
6	-in file3 -alg shift -key 25	file3.shift25 or file3.shift25.thai
7	-in file4 -alg shift -key 24 -out file4.enc
	-in file4.enc -alg shift -key 24 -mode dec	file4
8	-in file1 -alg unicode -key 999	file1.unicode999
9	-in file2 -alg unicode	file2
10	-in file2 -alg unicode -key 500	file2.unicode500
11	-in file3 -alg unicode -key 500	file3.unicode500
12	-in file4 -alg unicode -key 4999 -out file4.enc
	-in file4.enc -alg unicode -key 4999 -mode dec	file4

For Test 6 there are two possible solutions, depending on whether student code shifts only English letters or both English and Thai letters.