Question

我将此Java对象存储在List：

中

public class ExpressCheckout
{
    String currency;
    float amount;
    int quantity;
    String name;
    String description;
.......
}

如何从每个对象中将所有金额计入List？

Answer 1

做类似的事情：

public float sumAmounts(List<ExpressCheckout> myList){
  float total = 0.0f;
  for(ExpressCheckout item : myList){
    total += item.getAmount();
  }
  return total;
}

只需将它们放在for或foreach和总金额

中

Answer 2

如果您使用的是Java 8，那么使用流的非常简单的技术是：

list.stream().mapToDouble(ExpressCheckout::getAmount).sum();

Answer 3

警告，我使用Java 8并从逻辑上假设当你有多种货币时，你不能简单地将它们全部加起来。您可能需要按货币和总和进行分组。这为你提供了一个合理的想法

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class SomeClass {
    protected class ExpressCheckout {
        public String getCurrency() {
            return currency;
        }

        public void setCurrency(String currency) {
            this.currency = currency;
        }

        public float getAmount() {
            return amount;
        }

        public void setAmount(float amount) {
            this.amount = amount;
        }

        public int getQuantity() {
            return quantity;
        }

        public void setQuantity(int quantity) {
            this.quantity = quantity;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getDescription() {
            return description;
        }

        public void setDescription(String description) {
            this.description = description;
        }

        String currency;
        float amount;
        int quantity;
        String name;
        String description;

        public ExpressCheckout(String currency, float amount, int quantity, String name, String description) {
            this.currency = currency;
            this.amount = amount;
            this.quantity = quantity;
            this.name = name;
            this.description = description;
        }
    }

    public static void main(String[] args) {
        List<ExpressCheckout> expressCheckouts = new ArrayList<ExpressCheckout>();
        ExpressCheckout co1 = new SomeClass().new ExpressCheckout("USD", 20.01f, 2, "Item1", "Some item");
        ExpressCheckout co2 = new SomeClass().new ExpressCheckout("USD", 2.0f, 2, "Item1", "Some item");

        ExpressCheckout co3 = new SomeClass().new ExpressCheckout("INR", 100.01f, 2, "Item1", "Some item");

        ExpressCheckout co4 = new SomeClass().new ExpressCheckout("INR", 100.01f, 2, "Item1", "Some item");

        ExpressCheckout co5 = new SomeClass().new ExpressCheckout("INR", 200.01f, 2, "Item1", "Some item");
        expressCheckouts.add(co1);
        expressCheckouts.add(co2);
        expressCheckouts.add(co3);
        expressCheckouts.add(co4);
        expressCheckouts.add(co5);
        System.out
                .println(expressCheckouts.stream().collect(Collectors.groupingBy(SomeClass.ExpressCheckout::getCurrency,
                        Collectors.summingDouble(SomeClass.ExpressCheckout::getAmount))));

    }

}

从List中的对象计算所有金额

3 个答案: