根据另一个类中可用的参数对列表进行排序 [英] sort a List based on a parameter available in another class

问题描述

我在使用Java 比较器接口时遇到一些设计问题。

I have some design problems with Java Comparator Interface.

我有一个包含<$的类c $ c>设置一个简单的自定义数据结构：

I have a class which contains a Set of a simple custom data structure:

class data {  
    Long ID;  
    int Priority;  
    ...
}

ID 是唯一的，因此可以使用 ID‍‍‍‍ 来获取全部数据。

IDs are unique, so it is possible to get the whole data using ID‍‍‍‍‍.

和容器类：

class Container {
    Set<data> mySet = ...;
    List<Long> myList = ...;
    ...
}

出于某些不可避免的原因，我需要保持排序的数据 ID的排序后的列表。我需要列表要按 Priority 排序。

for some inevitable reasons, I need to keep a sorted List of data IDs in parallel. I need the List to be sorted by Priority.

因为，比较器应该比较优先级应该实现 Comparator< int> 。但是 List 仅包含 ID s和 Priority s不能直接使用。

Since, the Comparator should compare Prioritys it should implements Comparator<int>. But the List only contains IDs and the Prioritys are not available directly.

这是问题所在。 列表中只有 ID 。因此，Comparator类无法访问 Priority 。

This is the problem. There is only ID in the List. Therefore, the Comparator class has no access to Priority.

如何设计这种概念？

推荐答案

您可以使用闻起来像高阶函数的东西。也就是说，创建一个静态函数，该函数接受从Long到int（这是优先级）或数据的排序映射，并返回一个新的Comparator。

You could use something that smells like higher order functions. That is, make a static function that takes a map of sorts from Long to int (which is the priority) or data and returns a new Comparator.

Foo类具有静态方法 getComparator ，该方法需要使用Orange。 Orange是具有方法 getPriority 的类，该方法获取ID并返回相应的优先级。 getComparator 方法构造一个新的 Comparator 对象。新的 Comparator 对象的 compare 方法具有两个ID。它会查找两个ID的相应优先级并进行比较。

The class Foo has a static method getComparator which takes an Orange. An Orange is a class that has a method getPriority which takes an ID an return the corresponding priority. The getComparator method constructs a new Comparator object. The new Comparator object's compare method takes two IDs. It looks up the corresponding priorities of the two IDs and compares them.

public interface Orange {
    // Looks up id and returns the corresponding Priority.
    public int getPriority(Long id);
}

public class Foo {
    public static Comparator<Long> getComparator(final Orange orange) {
        return new Comparator<Long>() {
            public int compare(Long id1, Long id2) {
                // Get priority through orange, or
                // Make orange juice from our orange.
                // You may want to compare them in a different way.
                return orange.getPriority(id1) - orange.getPriority(id2);
        };
    }
}

我的Java有点生锈，所以代码可能是有缺陷的。

My java is a bit rusty so the code may be flawed. The general idea should work, though.

用法：

// This is defined somewhere. It could be a local variable or an instance
// field or whatever. There's no exception (except is has to be in scope).
Collection c = ...;
...
Orange orange = new Orange() {
    public int getPriority(Long id) {
        // Insert code that searches c.mySet for an instance of data
        // with the desired ID and return its Priority
    }
};
Collections.sort(c.myList, Foo.getComparator(orange));

我没有举一个橘子看起来的例子。

I have not given an example on how an Orange could look.

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