Java封装的真正作用与实战应用思路

private BigDecimal balance = BigDecimal.ZERO;

public void deposit(BigDecimal amount) {
    if (amount.compareTo(BigDecimal.ZERO) 

public class OrderService {

    private InventoryService inventoryService;
    private OrderRepository orderRepository;

    public Order placeOrder(OrderRequest request) {
        validateRequest(request);
        checkInventory(request.getItems());
        
        Order order = createOrder(request);
        reduceInventory(request.getItems());
        
        orderRepository.save(order);
        return order;
    }

    private void validateRequest(OrderRequest request) { ... }
    private void checkInventory(List items) { ... }
    private void reduceInventory(List items) { ... }
}

public class Order {
    private String status;

    public void cancel() {
        if (!canCancel()) {
            throw new IllegalStateException("当前状态不允许取消");
        }
        this.status = "CANCELLED";
    }

    public boolean canCancel() {
        return "UNPAID".equals(status) || "PAID".equals(status);
    }

    public boolean isShippable() {
        return "PAID".equals(status);
    }
}