Comparison 、IComparer

一个是委托，一个是接口，

// Summary:
// Defines a method that a type implements to compare two objects.
//
// Type parameters:
// T:
// The type of objects to compare.This type parameter is contravariant. That
// is, you can use either the type you specified or any type that is less derived.
// For more information about covariance and contravariance, see Covariance
// and Contravariance in Generics.
public interface IComparer<in T>
{
// Summary:
// Compares two objects and returns a value indicating whether one is less than,
// equal to, or greater than the other.
//
// Parameters:
// x:
// The first object to compare.
//
// y:
// The second object to compare.
//
// Returns:
// A signed integer that indicates the relative values of x and y, as shown
// in the following table.Value Meaning Less than zerox is less than y.Zerox
// equals y.Greater than zerox is greater than y.
int Compare(T x, T y);
}

定义如下：如果返回负数，表示x<y，如果返回正数，表示x>y，在排序中可以这么理解，

x<y，返回负数，表示承认x比y小，这样就能排出升序的效果。

deductionStrategyEntitiesTmp.Sort((x, y) =>
{
if (x.StartAmount > y.StartAmount) return -1;
else if (x.StartAmount < y.StartAmount) return 1;
else return 0;
}); //扣减金额递减

  //分数由大变小

Collections.sort(promotionActivitiesResult, new Comparator<PromotionActivity>() {
    @Override
    public int compare(PromotionActivity o1, PromotionActivity o2) {
        return o2.getSortScore() > o1.getSortScore() ? 1 : o2.getSortScore() < o1.getSortScore() ? -1 : 0;
    }
});