Encryption Algorithm Question

Programming Questions

andrewgie..

Encryption Algorithm Question

in Programming Questions • 11 months ago

Hey all,

I cannot figure out what the problem is with this program. I want to, for each of the characters in the input, obtain the appropriate replacement, and fill a second char array with the results. This is what I have, and the highlighted line returns a NullPointerException.

char ec[][] = {{'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'},
{'O', 'N', 'E', 'W', 'R', 'D', 'S', 'T', 'Y', 'A', 'B', 'C', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'P', 'Q', 'U', 'V', 'X', 'Z'}};
String input = "ANDREW";
String encryption;
char[] tempChars = input.toCharArray();
char[] afterChange;
void setup() {
println(ec[0][0]);
println(ec[1][0]);
for(int pos = 0; pos < tempChars.length; pos++) {
for(int scroll = 0; scroll < 26; scroll++) {
if(tempChars[pos] == ec[0][scroll]) {
afterChange = append(afterChange, ec[1][scroll]);
} else {
}
}
}
encryption = afterChange.toString();
println(encryption);
}
void draw() {
}

andrewgies17

Replies(9)

GoToLoop

Re: Encryption Algorithm Question

11 months ago

Hello!
I did a little experiment on turning char[] afterChange into ArrayList<Character> afterChange = new ArrayList();
And it seemed to have worked! Check it out:

private static final char ec[][] = {
    {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
    }
    , 
    {
        'O', 'N', 'E', 'W', 'R', 'D', 'S', 'T', 'Y', 'A', 'B', 'C', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'P', 'Q', 'U', 'V', 'X', 'Z'
    }
};

private static final String input = "ANDREW";
private static final char[] tempChars = input.toCharArray();

private static final ArrayList<Character> afterChange = new ArrayList();

void setup() {

    noLoop();
    println(ec[0][0]);
    println(ec[1][0]);

    for (int pos=0, len=tempChars.length; pos<len; pos++)
        for (byte scroll=0; scroll<26; scroll++)

            if ( tempChars[pos] == ec[0][scroll] )
                afterChange.add( ec[1][scroll] );

    String encryption = afterChange.toString();
    println(encryption);
}

andrewgie..

Re: Encryption Algorithm Question

11 months ago

So, I'm very new to array lists. It's basically a user friendly array, correct? To make an array list, the constructor would look like so

ArrayList<Type> arrayListName = new ArrayList<Type>();

Right? If I would create an array list of my own class it would look the same right? Also, can I make multi-dimensional ArrayLists? Thanks.

andrewgies17

GoToLoop

Re: Encryption Algorithm Question

11 months ago

We're in the same boat. I'm new to ArrayList<> as well!
I always prefer the traditional array[] type myself.

But array[] type is more appropriate when you know exactly the dimensions you're gonna use before hand, like:
int[][] myArray = new int[20][10];
color[] myColors = { #FF0000, #00FFFF, #A0A0A0 };

When dimensions change during runtime, ArrayList is the way to go. Even though traditional arrays have the append() method, which i dunno how to use it right yet!

GoToLoop

Re: Encryption Algorithm Question

11 months ago

Here's a example w/ classes using ArrayList<> -> Evolution Sim
Dunno if ArrayList<> can have more than 1 dimension though.

benja

Re: Encryption Algorithm Question

11 months ago

ArrayLists are one-dimensional, but it is possible to create an arraylist of arraylists. It works well but the syntax is a little odd. Soemthing like this:

// create an arraylist of arraylists
ArrayList<ArrayList<Character>> myList = new ArrayList<ArrayList<Character>>();

// add array-lists to the outer array-list
for (int i = 0; i< 5; i++) {
myList.add(new ArrayList<Character>());
}

// add a value to an inner arraylist
myList.get(0).add('c');

// access a value from an inner arraylist
println(myList.get(0).get(0));

quarks

Re: Encryption Algorithm Question

11 months ago

it is possible to solve this problem without using any ArrayList or char array and still handle input strings of any length. The answer is to use the StringBuilder class to construct the string. The code below does the job and puts in a ? when it can't find the character in the input character list.

String inchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String outchars = "ONEWRDSTYABCFGHIJKLMPQUVXZ";
String input = "ANDREW";
StringBuilder output;
String encryption;
void setup() {
output = new StringBuilder();
for (int i = 0; i < input.length(); i++) {
char c = input.charAt(i);
int p = inchars.indexOf(c);
if (p >= 0) // found c
output.append(outchars.charAt(p));
else // did not find c
output.append('?');
}
encryption = output.toString();
println(input + " >> " + output);
}

v.k.

Re: Encryption Algorithm Question

11 months ago

Does this "private final static" calling really makes things faster?

quarks

Re: Re: Encryption Algorithm Question

11 months ago

In this program the answer is no.

private is an access modifier which only has an effect if you have more than one class
static indicates that the variable belongs to a class rather than an instance of a class

So the first two only have any real significance if you start creating your own classes.

final means that the variable is in fact a constant so can't be changed later.

In this particular instance we have

final String input = "ANDREW";
final char[] tempChars = input.toCharArray();

which means these statements will generate errors

input = "QUARKS;;
tempChars = new chars[10];

but this statement is legal because the array reference is constant not the elements in the array

tempChars[1] = '?';

v.k.

Re: Encryption Algorithm Question

11 months ago

I see, but in case you got some classes you made, there will be difference in performance? Even if minimal?

Top Reply