如果有库存，则按价格升序对产品进行排序

Question

我正在做一个 Java 比较练习，要求我按产品是否有货对产品进行排序，然后按价格升序排列。有关更多详细说明，请阅读 PriceStockComparator class.

中的评论

import java.util.Comparator;
import java.util.Collections;

public class Product {
    private String name;
    private int priceCents;
    private int stockLevel;

    public Product(String name, int priceCents, int stockLevel) {
        this.name = name;
        this.priceCents = priceCents;
        this.stockLevel = stockLevel;
    }

    @Override
    public String toString() {
        return this.name + ": " + this.stockLevel + " @ $" + this.priceCents / 100.0;
    }

    /**
     * This comparator should sort products by whether or not they are in stock,
     * then in ascending order by their price.
     *
     * After sorting, products that have a positive stock level should appear
     * before products that have a stock level of 0. If two products being
     * sorted are either 1) both in stock; or 2) both out of stock, they
     * should then be sorted based on their price in ascending order.
     */
    static class PriceStockComparator implements Comparator<Product> {
        @Override
        public int compare(Product p1, Product p2) {
            // write your code here
            return Integer.compare(p1.stockLevel, p2.stockLevel);
        }
    }
}

我的程序有 4 个错误

=> java.lang.AssertionError: expected:<[Apple: 5 @ .0, Bottled Water: 2 @ .0, Donut: 7 @ .0]> but was:<[Bottled Water: 2 @ .0, Apple: 5 @ .0, Donut: 7 @ .0]>
=> java.lang.AssertionError: expected:<[Apple: 5 @ .0, Bottled Water: 2 @ .0, Donut: 7 @ .0, Fish: 3 @ .0, Crackers: 0 @ .0, Eggs: 0 @ .0]> but was:<[Crackers: 0 @ .0, Eggs: 0 @ .0, Bottled Water: 2 @ .0, Fish: 3 @ .0, Apple: 5 @ .0, Donut: 7 @ .0]>
=> java.lang.AssertionError: expected:<[Crackers: 0 @ .0, Eggs: 0 @ .0]> but was:<[Eggs: 0 @ .0, Crackers: 0 @ .0]>
=> java.lang.AssertionError: expected:<[Donut: 7 @ .0, Fish: 3 @ .0, Eggs: 0 @ .0]> but was:<[Eggs: 0 @ .0, Fish: 3 @ .0, Donut: 7 @ .0]>

那是因为我排序了库存水平，但我不能先把它设为正数，而且我没有按价格升序排序。我不认为我可以在这里使用两个 compareTo() 并且我打算使用 Collection.sort 来对价格的升序进行排序。但我不知道该怎么做。如果有人可以提供帮助，我会很好。谢谢！

Answer 1

您可以按如下方式编写您的 compareTo 方法：

public int compare(Product p1, Product p2) {

    //If both the products are in stock or are not in stock
    // we can compare them on price
    if(p1.getStockLevel()>0 && p2.getStockLevel()>0 || 
            p1.getStockLevel()<=0 && p2.getStockLevel()<=0)
        return Integer.compare(p1.getPriceCents(), p2.getPriceCents());
    // If the first product is not in stock then we move it down the list
    // by returning a -1
    else if(p1.getStockLevel()>0 && p2.getStockLevel()<=0)
        return -1;
    // If second product is not in stock but first one
    else 
        return 1;

}

Answer 2

您可以使用 Java 8 个 lambda 表达式。编译器能够推断类型定义。如果您的对象产品在列表中，您可以执行如下操作...

List<Product> products = new ArrayList<>();
Collections.sort(products, (a,b) -> a.priceCents - b.priceCents);

如果您需要参考，Baeldung 有一个很好的页面，其中包含一些您可以借鉴的示例。

如果有库存，则按价格升序对产品进行排序

Sort product if in stock then in ascending order in price

java

sorting

compareto