values of protected arrays on superclass get changed unexpectedly

I'm coding a chess engine using bitboards and I wanna make an extensible API for the bitboards initializer, that would allow me to add more variants like chess960 in future.

So i came up with the following abstract superclass, which gives an uniform interface for all kind of initializers: it allocates the arrays used to store the bitboards and then calls the abstract method init() that has to be implemented by any subclass, inside there the bitboards should be created and assigned to the respective array

public abstract class BitboardInitializer {
 
    private static final int NUMBER_OF_PLAYERS = 2;
 
    protected long[] pawnsPositions, knightsPositions, bishopsPositions,
            rooksPositions, queenPositions, kingPositions;
 
    protected BitboardInitializer() {
        pawnsPositions = knightsPositions = bishopsPositions =
                rooksPositions = queenPositions = kingPositions = new long[NUMBER_OF_PLAYERS];
        init();
    }
 
    protected abstract void init();
 
    public long getPawnsPositionsAs(int side) {
        return pawnsPositions[side];
    }
 
    public long getKnightsPositionsAs(int side) {
        return knightsPositions[side];
    }
 
    public long getBishopsPositionsAs(int side) {
        return bishopsPositions[side];
    }
 
    public long getRooksPositionsAs(int side) {
        return rooksPositions[side];
    }
 
    public long getQueenPositionsAs(int side) {
        return queenPositions[side];
    }
 
    public long getKingPositionsAs(int side) {
        return kingPositions[side];
    }
}

An implementation to initialize standard chess bitboards, it simply assign the hard-coded bitboards values because standard chess starts always in one way. Side.White and Side.Black are two static final fields used as array indexes to avoid inconsistence. white = 0, black = 1:

public final class StandardChessInitializer extends BitboardInitializer {
 
    public StandardChessInitializer() {
        super();
    }
 
    protected void init() {
        pawnsPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_11111111_00000000L;
        pawnsPositions[Side.BLACK] =
                0b00000000_11111111_00000000_00000000_00000000_00000000_00000000_00000000L;
        knightsPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_01000010L;
        knightsPositions[Side.BLACK] =
                0b01000010_00000000_00000000_00000000_00000000_00000000_00000000_00000000L;
        bishopsPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_00100100L;
        bishopsPositions[Side.BLACK] =
                0b00100100_00000000_00000000_00000000_00000000_00000000_00000000_00000000L;
        rooksPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_10000001L;
        rooksPositions[Side.BLACK] =
                0b10000001_00000000_00000000_00000000_00000000_00000000_00000000_00000000L;
        queenPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_00010000L;
        queenPositions[Side.BLACK] =
                0b00010000_00000000_00000000_00000000_00000000_00000000_00000000_00000000L;
        kingPositions[Side.WHITE] =
                0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_00001000L;
        kingPositions[Side.BLACK] =
                0b00001000_00000000_00000000_00000000_00000000_00000000_00000000_00000000L;
    }
}

The problem is that by calling any superclass' getter method I get binary 1000 for white (index 0) and 100000000000000000000000000000000000000000000000000000000000 for black (index 1) instead of the assigned values

An explanation of this strange behaviour would be highly appreciated, thanks in advance.

The problem is in the BitboardInitializer constructor, where you are initializing all of your array references to point to the same array:

protected BitboardInitializer() {
    pawnsPositions = knightsPositions = bishopsPositions =
            rooksPositions = queenPositions = kingPositions = new long[NUMBER_OF_PLAYERS];
    init();
}

Should be:

protected BitboardInitializer() {
    pawnsPositions = new long[NUMBER_OF_PLAYERS];
    knightsPositions = new long[NUMBER_OF_PLAYERS];
    bishopsPositions = new long[NUMBER_OF_PLAYERS];
    rooksPositions = new long[NUMBER_OF_PLAYERS];
    queenPositions = new long[NUMBER_OF_PLAYERS];
    kingPositions = new long[NUMBER_OF_PLAYERS];
    init();
}