ShoppingBasketWithState.java

// shopping basket with state pattern
public static class ShoppingBasket {
    private String orderNo;
    private List<String> articleNumbers = new ArrayList<>();
    private UpdateState state = UpdateState.UPDATEABLE;
    public void add(String articleNumber) {
        articleNumbers.add(state.set(articleNumber));
    }
    public String getOrderNo() {
        return orderNo;
    }
    public void setOrderNo(String orderNo) {
        this.orderNo = state.set(orderNo);
    }
    public void order() {
        // some ordering logic and if succeeded, change state
        state = UpdateState.READONLY;
    }
}