英文:
Sorting list of objects according the changeable object field
问题
我有一个产品列表。我想根据它们的数量递减地对产品进行排序。
public class Product {
String name;
int quantity;
Product(String name, int quantity) {
this.name = name;
this.quantity = quantity;
}
}
默认情况下，列表中有4个数量为0的产品。
List<Product> products = new ArrayList();
products.add(new Product("Book", 0));
products.add(new Product("Table", 0));
products.add(new Product("Chair", 0));
products.add(new Product("Pen", 0));
此外，用户可以通过网页界面逐个增加或减少数量（通过点击每个产品旁边的增加或减少按钮）。
例如，如果用户增加“Pen”产品的数量，则应将“Pen”产品重新定位到列表顶部。
每次增加或减少过程中，我需要重新对列表进行排序。然而，每次增加或减少过程中运行排序算法非常低效，特别是如果列表中有很多项。
我尚未使用任何排序算法。但我相信，如果列表中的项过多，仅发生一次增加，那么整个列表都必须重新排序。我认为这是低效的，所以我想知道是否有另一种解决这种问题的方法。
那么，如何对这种类型的列表进行排序呢？
英文:
I have a Product list. I want to sort the products decreasingly according to their quantities.
public class Product {
String name;
int quantity;
Product(String name, int quantity) {
this.name=name;
this.quantity=quantity
}
}
By default there are 4 Products in the list with 0 quantity.
List<Product> products = new ArrayList();
products.add(new Product("Book",0));
products.add(new Product("Table",0));
products.add(new Product("Chair",0));
products.add(new Product("Pen",0));
Also, quantities can be incremented or decremented one by one by the user from the web UI (by clicking a increment or decrement button which are located besides of every product)
For example, if user increment the "Pen" product quantity, then the "Pen" product should be relocated to top of the list .
Every, increment or decrement process, I need to re-sort the list. However, running a sorting algorithm every increment or decrement process is very inefficient especially if there are a lot of items in the list.
I haven't use any sorting algorithm yet. But I believe that, if there are too many items in the list and an increment occurred only one product, then all list have to be sorted again. I think, this is inefficient so I am asking that is there another way for this kind of problem.
So, how can sort these kind of a list?
答案1
得分: 0
Java 8的列表排序方式。内部使用归并排序算法。
products.sort(Comparator.comparing(Product::getQuantity).reversed());
或者
products.sort(Comparator.comparing(Product::getQuantity, Comparator.reverseOrder()));
流（Stream）示例
products.stream()
.sorted(Comparator.comparing(Product::getQuantity, Comparator.reverseOrder()))
.forEach(System.out::println);
英文:
Java 8 way of sorting a list. Internally it is merge sort.
products.sort(Comparator.comparing(Product::getQuantity).reversed());
OR
products.sort(Comparator.comparing(Product::getQuantity, Comparator.reverseOrder()));
Stream Example
products.stream()
.sorted(Comparator.comparing(Product::getQuantity, Comparator.reverseOrder()))
.forEach(System.out::println);
答案2
得分: 0
我们在Collections类中有一个sort方法，可以使用ASC顺序对产品进行排序：
Collections.sort(products, Comparator.comparing(Product::getQuantity));
而对于DESC，我们需要调用reversed方法：
Collections.sort(products, Comparator.comparing(Product::getQuantity).reversed());
英文:
We have a sort method in the Collections class and can sort products with ASC order like:
Collections.sort(products, Comparator.comparing(Product::getQuantity));
And for DESC, we need to invoke the reversed method:
Collections.sort(products, Comparator.comparing(Product::getQuantity).reversed());
专注分享java语言的经验与见解，让所有开发者获益！
评论