Java 排序集合实现，允许许多相等的值

Question

我尝试使用TreeSet:

Comparator<Product> pc = (p1, p2) -> ((Double) p1.getPrice()).compareTo(p2.getPrice());
Set<Product> products = new TreeSet<>(pc);
products.add(new Product(10));
products.add(new Product(10));

但问题是，就比较器而言，它不能包含多个相等的值，因此 products 集中只有一个产品。

我需要一些 Collection 实现，它将对新插入的值进行排序，允许许多相等(就比较器而言)值，并且具有插入复杂性 log(n) (可能是基于树的实现)

Answer 1

JDK 中符合您确切要求的类是 PriorityQueue 。来自文档:

An unbounded priority queue based on a priority heap. The elements of the priority queue are ordered according to their natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.

还有

Implementation note: this implementation provides O(log(n)) time for the enqueuing and dequeuing methods (offer, poll, remove() and add); linear time for the remove(Object) and contains(Object) methods; and constant time for the retrieval methods (peek, element, and size).

<小时/>

您还可以继续使用TreeSet，但提供一个Comparator来给出唯一的答案。例如，如果您的产品有一个唯一的名称:

Comparator<Product> pc = Comparator.comparing(Product::getPrice)
                         .thenComparing(Comparator.comparing(Product::getName));

请注意使用 Comparator.comparing 而不是 lambda - 它更简洁、更健壮。