何时在Java中使用Enum或Collection

public enum OrderStatus {
    PLACED,
    PROCESSING,
    SHIPPED,
    DELIVERED,
    CANCELLED
}

import java.util.ArrayList;
import java.util.List;

public class Order {
    private String orderId;
    private List<OrderItem> orderItems;

    public Order(String orderId) {
        this.orderId = orderId;
        this.orderItems = new ArrayList<>();
    }

    public void addOrderItem(OrderItem orderItem) {
        this.orderItems.add(orderItem);
    }

    // 其他代码
}