我有一个应用程序,用户在其中向我提供字段名称,例如name
或costInCents
,我必须按该字段排序。我有保证字段名称正确的方法。这个应用程序引起的麻烦是,我无法简单地创建类Comparable
并实现特定的compareTo()
,因为使用自定义实现,compareTo()
我需要知道在实现时要使用哪些字段/方法。
因此,为了实现此目标,我尝试使用反射以使字段与其访问者匹配。这是我想做的MWE。
类Product
是一个简单的POJO类,我想成对比较其实例:
public class Product
{
final String name;
final Integer quantity;
final Long costInCents;
public Product(final String name, final Integer quantity, final Long costInCents)
{
this.name = name;
this.quantity = quantity;
this.costInCents = costInCents;
}
public String getName()
{
return name;
}
public Integer getQuantity()
{
return quantity;
}
public Long getCostInCents()
{
return costInCents;
}
}
而我的Main
课程,目前尚未完成:
public class Main {
public static void main(String[] args) {
final Product[] productArray =
{
new Product("Clorox wipes", 50, 700L),
new Product("Desk chair", 10, 12000L),
new Product("TV", 5, 30000L),
new Product("Bookcase", 5, 12000L),
new Product("Water bottle", 20, 700L),
};
// The following void methods are supposed to sort in-place with something like Arrays.sort() or Collections.sort(),
// but I am also open to solutions involving stuff like Stream::sorted() or similar ones, which return a sorted array.
sortByField(productArray, "costInCents");
sortByField(productArray, "name");
}
private void sortByField(final Product[] productArray, final String sorterFieldName)
{
final Field sorterField = getSorterField(sorterFieldName, LiteProduct.class); // Gets the Field somehow
final Method sorterAccessor = getSorterAccessor(sorterField, LiteProduct.class); // Given the Field, this is easy
Arrays.sort((Product p1, Product p2)->((Comparable<?>)sorterAccessor.invoke(p1)).compareTo(sorterAccessor.invoke(p2)) > 0); // Capture of ? instead of Object
}
}
不幸的是,该Arrays.sort()
行导致带有message的编译时错误Capture of ? instead of Object
。我曾尝试铸造的第二个参数Comparable<?>
,Comparable<? super sorterField.getType()
等等,没有运气。有想法吗?
可能是最好的方法-使用排序策略。无需反射,与更复杂的排序逻辑兼容:
Map<String, Comparator<Product>> sortingStrategies = new HashMap<>(){
{
put("costInCents", Comparator.comparingLong(p->p.costInCents));
put("quantity", Comparator.comparingLong(p->p.quantity));
put("name", Comparator.comparing(p->p.name));
}
};
private void sortByField(final Product[] productArray, final String sorterFieldName)
{
Arrays.sort(productArray, sortingStrategies.get(sorterFieldName));
}
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