java:集合对象根据某一个字段分组并求出另一个字段的和

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我不会秃头 2024-07-12 15:35:12 ©著作权

文章标签 java 文章分类 Java 后端开发 技术人为什么要写博客？

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1.假设我们有一个list对象。对象里边存放着预算编号、预算金额。


PurchasePlanDetailsBudgetPO purchasePlanDetailsBudgetPO = new PurchasePlanDetailsBudgetPO();
        purchasePlanDetailsBudgetPO.setBudgetNo("0000001");
        purchasePlanDetailsBudgetPO.setSelectionAmount(new BigDecimal(100));
        list.add(purchasePlanDetailsBudgetPO);
 
        PurchasePlanDetailsBudgetPO purchasePlanDetailsBudgetPO1 = new PurchasePlanDetailsBudgetPO();
        purchasePlanDetailsBudgetPO1.setBudgetNo("0000001");
        purchasePlanDetailsBudgetPO1.setSelectionAmount(new BigDecimal(100));
        list.add(purchasePlanDetailsBudgetPO1);
 
        PurchasePlanDetailsBudgetPO purchasePlanDetailsBudgetPO2 = new PurchasePlanDetailsBudgetPO();
        purchasePlanDetailsBudgetPO2.setBudgetNo("0000002");
        purchasePlanDetailsBudgetPO2.setSelectionAmount(new BigDecimal(100));

2.以上new了三个对象，有两个编号是一样的。接下来可以对编号进行分组然后求出来金额的总和。

Map<String, BigDecimal> listMap = list.stream().collect(
                Collectors.groupingBy(
                        PurchasePlanDetailsBudgetPO::getBudgetNo,
                        Collectors.reducing(BigDecimal.ZERO, PurchasePlanDetailsBudgetPO::getSelectionAmount,  BigDecimal::add)));

以上就是分组求和，比较简单，完全可以通过java8中的stream来实现