How to list all possible moves in connect four game

Question

I am making an AI following this article. The basic idea is using bitboards to make a extremely fast protocol for making modifications to the board and permutating through possible game outcomes.

But the article is written in python and I had trouble following the initial bitboard setup. I went to the github readme they reference in hopes to develop the framework for my AI and then worry about alpha-beta pruning and the machine learning later. Essentially I got past the methods for checkWin, makeMove, and undoMove and estabilished the required fields for the height of columns, moves, the count of moves, and the array of long variables representing the bitboards for the players.

But I am currently stuck at the generate moves method because it tries to initialize all the values at the top of the bitboard outside of the columns. But in java I can't seem to do this: it just gives me the error this literal type is out of range for type long. Additionally seeing as moves is a int[] I'm not sure how to use moves.push(col). Because that gives the error cannot invoke push(int). Below you will find the broken listMoves method and my current code and I would be very appreciative if anyone could tell me some things I might be doing wrong in my code and or how to fix the listMoves method. Cheers!

   private int[] listMoves() {
        int[] moves;
        long TOP = 1000000_1000000_1000000_1000000_1000000_1000000_1000000L;
        for(int col = 0; col <= 6; col++) {
            if ((TOP & (1L << height[col])) == 0) moves.push(col);
        }
        return moves;
    }

My code

 public class EConnectFour {
    private int[] height = {0, 0, 0, 0, 0, 0, 0};
    private int[] moves = new int[42]; // add size 
    private int counter = 0;

    private long[] bitBoard = new long[2];



    public static void main(String[] args) {



    }

    private char[][] getGameState() {
        // add code to get current gamestate 
        return new char[0][0];
    }


    private boolean isWin(long bitBoard) {
        int[] directions = {1, 7, 6, 8};
        long bb;
        for(int direction : directions) {
            bb = bitBoard & (bitBoard >> direction);
            if ((bb & (bb >> (2 * direction))) != 0) return true;
        }
        return false;
    }

    private void makeMove(int column) {
        long move = 1L << height[column]++;
        bitBoard[counter & 1] ^= move; 
        moves[counter++] = column;  
    }

    private void undoMove() {
        int column = moves[--counter];
        long move = 1L << --height[column];
        bitBoard[counter & 1] ^= move;
    }
}