Question

I am developing desktop app in Java 7. I have here a situation. At the method below

private synchronized void decryptMessage
    (CopyOnWriteArrayList<Integer> possibleKeys, ArrayList<Integer> cipherDigits)
{
    // apply opposite shift algorithm:
    ArrayList<Integer> textDigits = shiftCipher(possibleKeys, cipherDigits);

    // count CHI squared statistics:
    double chi = countCHIstatistics(textDigits);

    if(chi < edgeCHI) // if the value of IOC is greater or equal than that
    {
        System.err.println(chi + " " + possibleKeys + " +");
        key = possibleKeys; // store most suitable key
        edgeCHI = chi;
    }       
}

I count the value called ‘chi’ and based on that if ‘chi’ is less than ‘edgeCHI’ value I save the key at instance variable. That method is invoked by some threads, so I enforce synchronization.

When all the threads complete the program continues to execute by passing control to a method which controls the sequence of operations. Then this line has been executed at that method:

System.err.println(edgeCHI+" "+key+" -"); 

It prints correct value of ‘chi’, as has been printed the last value of ‘chi’ at decryptMessage method, but the value of key is different. The ‘decryptMessage’ method has been invoked by threads which generate key values.

I store the key value as global variable
private volatile CopyOnWriteArrayList<Integer> key = null; // stores the most suitable key for decryption.
Why do I have two different key values? The values itself are not important. The matter is that the value of key printed at the last call at ‘decryptMessage’ method (when chi < edgeCHI) must match the one printed at the method which controls the flow of operations.
This is how you create threads:

for(int y = 0; y < mostOccuringL.length; y++){// iterate through the five most frequent letters
                for(int i = (y + 1); i < mostOccuringL.length; i++ ){//perform letter combinations
                    int [] combinations = new int[2];
                    combinations[0] = y;
                    combinations [1] = i;                   
                    new KeyMembers(""+y+":"+i ,combinations, keywords, intKeyIndex, cipherDigits).t.join();
                }
            }   

Within run method you invoke decryptMesssage method in order to identify most feasible decryption key.
I have been trying to figure out what is the prob for two days, but I don’t get it.
Suggestions?

Answer 1

Solution has been found. I just changed CopyOnWriteArrayList data type into ArrayList at the point where field variable gets correct key. It works as expected now.