Array in Java which has Javascript array-like nature

Question

I have some reference code which is written in Javascript and I am trying to port it to Java.

The problem I have with the porting is that I don't have anything in Java which can be used as stack and normal array at the same time. The reference code uses an array object which can act as a normal array and also like a stack.

Is there anything which I can use to resolve my problem?

Reference Code:

var ascii85 = function (input) {
    // input: Array: an array of numbers (0-255) to encode
    var result = [],
        reminder = input.length % 4,
        length = input.length - reminder;
    c(input, length, result);
    if (reminder) {
        var t = input.slice(length);
        while (t.length < 4) {
            t.push(0);
        }
        c(t, 4, result);
        var x = result.pop();
        if (x == "z") {
            x = "!!!!!";
        }
        result.push(x.substr(0, reminder + 1));
    }
    return result.join("");
};

The code of c function is below:

var c = function (input, length, result) {
    var i, j, n, b = [0, 0, 0, 0, 0];
    for (i = 0; i < length; i += 4) {
        n = ((input[i] * 256 + input[i + 1]) * 256 + input[i + 2])
            * 256 + input[i + 3];
        if (!n) {
            result.push("z");
        } else {
            for (j = 0; j < 5;
                b[j++] = n % 85 + 33, n = Math.floor(n / 85)
            );
        }
        result.push(String.fromCharCode(
            b[4], b[3], b[2], b[1], b[0]));
    }
};

Did an old school C programmer write that code? It's not very...JavaScript-y. — VLAZ
– VLAZ, Commented Apr 5, 2015 at 19:35
Also "stack and normal array at the same time" - I'm trying to see what of both is needed here, but until then on a hunch - would a List work? It implements the Stack interface and you can do list.get(n). — VLAZ
– VLAZ, Commented Apr 5, 2015 at 19:37

Radiodef · Accepted Answer · 2015-04-05 20:34:26Z

1

Javascript Array.prototype.push corresponds to List#add:

t.add(0);

List has no analog for Array.prototype.pop but you can remove the last element:

result.remove(t.size() - 1);

So the code could therefore be converted to use ArrayList, for example.

LinkedList allows push/pop as well as access by index but its indexing is O(n).

There is also Stack which has push/pop and O(1) indexing, but it's a subclass of Vector which new code is generally steered away from using. (Basically Vector's operations are synchronized for thread safety, which is a pointless overhead if the Stack isn't shared between threads. Vector is superseded by Collections.synchronizedList in this regard, so Stack has a very niche feature set.)

I also don't see a problem with doing something like the following:

public class MyList<E> extends ArrayList<E> {
    public E pop() {
        return this.remove(this.size() - 1);
    }
}

It doesn't break Liskov Substitution Principle (still behaves as an ArrayList).

edited Apr 5, 2015 at 20:34

answered Apr 5, 2015 at 19:44

Radiodef

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3 Comments

VLAZ Over a year ago

Sorrry, yes - I was looking at a different implementation of List

Sunny Over a year ago

I think Vid's solution is also useful but have not tried it but I think it should also work. Thanks for your solutions too. :)

Radiodef Over a year ago

@Sunny I've mentioned Stack in my answer. Of course whatever you do is up to you. ; )

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