Java 使用许多属性的对象 Comparable

Question

我有一些订单要在配送路线中装卸，一条路线可以分配一个 OrderDocument 给它装货、卸货或两者兼而有之。每个订单文件都按分配的路线中的索引排序。所以 class 看起来像这样：

class OrderDocument implements Comparable<ModelTask>{
    int order_id;  // The document ID
    int route_load_id;  // The route this order is assigned to be loaded
    int route_unload_id;  // The route this order is assigned to be loaded, may be same as route_load_id and viceversa
    int route_load_index;  // The index order in load route
    int route_unload_index;  // The index order in unload route
}

然后我有路线 class:

class Route{
    int id; // ID of route, this value should be in OrderDocument.route_load/unload_id
    ArrayList<OrderDocument> orders;  // **I WANT TO SORT THIS LIST**
   ...

所以，我有一个创建 Route 实例并将 OrderDocument 对象添加到其 orders ArrayList 的函数，因此列表应该包含 Route.id 在 route_load_id 或 route_unload_id

主要问题

如果路由 ID 在 load_id 或 unload_id 中，我需要此列表按 load/unload 索引排序。实际上我有以下 Comparator 方法但没有用。

private class OrdersComparable implements Comparator<OrderDocument>{
    @Override
    public int compare(OrderDocument x, OrderDocument y) {
        if (x.route_load_id == y.route_load_id)
            return x.route_load_index - y.route_load_index;
        else if (x.route_load_id == y.route_unload_id)
            return x.route_load_index - y.route_unload_index;
        else if (x.route_unload_id == y.route_load_id)
            return x.route_unload_index - y.route_load_index;
        else if (x.route_unload_id == y.route_unload_id)
            return x.route_unload_index - y.route_unload_index;
        else
            return 0;
    }
}

例子

43号公路订单4个，待装2个，待卸4个。

OrderDocument('order_id':1, 'route_load_id':43, 'route_unload_id':null, 'route_load_index':0, 'route_unload_index':null)
OrderDocument('order_id':2, 'route_load_id':43, 'route_unload_id':null, 'route_load_index':2, 'route_unload_index':null)
OrderDocument('order_id':3, 'route_load_id':null, 'route_unload_id':43, 'route_load_index':null, 'route_unload_index':1)
OrderDocument('order_id':1, 'route_load_id':null, 'route_unload_id':43, 'route_load_index':null, 'route_unload_index':3)

order_id 的实际订单：1、2、3、1

order_id 要求的顺序：1、3、2、1

Answer 1

如果你使用的是null值（以及相应的可空类型），你必须检查你的条件不要比较空值，否则会满足一个不希望的条件：

class OrderDocument implements Comparable<ModelTask> {
    int order_id;  // The document ID
    Integer route_load_id;  // The route this order is assigned to be loaded
    Integer route_unload_id;  // The route this order is assigned to be loaded, may be same as route_load_id and viceversa
    Integer route_load_index;  // The index order in load route
    Integer route_unload_index;  // The index order in unload route
}

class OrdersComparable implements Comparator<OrderDocument> {
@Override
public int compare(OrderDocument x, OrderDocument y) {
    if (x.route_load_id == y.route_load_id && x.route_load_id != null)
        return Integer.compare(x.route_load_index, y.route_load_index);

    if (x.route_load_id == y.route_unload_id && x.route_load_id != null)
        return Integer.compare(x.route_load_index, y.route_unload_index);

    if (x.route_unload_id == y.route_load_id && x.route_unload_id != null)
        return Integer.compare(x.route_unload_index, y.route_load_index);

    if (x.route_unload_id == y.route_unload_id && x.route_unload_id != null)
        return Integer.compare(x.route_unload_index, y.route_unload_index);

    return 0;
}
}

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