RingBuffer

public class RingBuffer {
    private int capacity;
    private final BigDecimal[] data;
    private int lastEntryIndex;

    public RingBuffer(int capacity) {
        this.capacity = capacity;
        this.data = new BigDecimal[capacity];
    }

    public void setElement(BigDecimal element) {
        int oldestElementIndex = getOldestElementIndex();
        if (!isFull()) {
            for (int i = 0; i < data.length; i++) {
                if (data[i] == null) {
                    data[i] = element;
                    lastEntryIndex = i;
                    break;
                }
            }
        } else {
            data[oldestElementIndex] = element;
        }
    }

    public int getOldestElementIndex() {
        int oldestEntryIndex;
        if ((lastEntryIndex == data.length - 1) || !isFull()) {
            oldestEntryIndex = 0;
        } else oldestEntryIndex = lastEntryIndex + 1;
        return oldestEntryIndex;
    }

    public boolean isFull() {
        boolean hasNoNulls = false;
        for (int i = 0; i < data.length; i++) {
            hasNoNulls = data[i] != null;
        }
        return hasNoNulls;
    }

    public int getCapacity() {
        return capacity;
    }

    public void setCapacity(int capacity) {
        this.capacity = capacity;
    }

    public BigDecimal[] getData() {
        return data;
    }

}