Java 双指针在实际项目中的应用

背景说明

最近在做财务相关的系统，对账单核销预付款
从技术角度来看就是将两个数组进行合并

对账单核销预付款前提条件：

1. 对账单总金额必须等于未核销金额

数据示例

对账单数据

预付款数据

结果数据

通过分析可以使用JAVA双指针算法可以实现这个需求
双指针主要用于遍历数组，两个指针指向不同的元素，从而协同完成任务。

代码实现

public static void main(String[] args) {
    class Info {
        private String formId;
        private BigDecimal amount;
    
        public String getFormId() {
            return formId;
        }
    
        public void setFormId(String formId) {
            this.formId = formId;
        }
    
        public BigDecimal getAmount() {
            return amount;
        }
    
        public void setAmount(BigDecimal amount) {
            this.amount = amount;
        }
    }
    
    List<Info> billBatchlist = new ArrayList<>();
    Info info = new Info();
    info.setFormId("B0001");
    info.setAmount(new BigDecimal(100));
    billBatchlist.add(info);
    info = new Info();
    info.setFormId("B0002");
    info.setAmount(new BigDecimal(80));
    billBatchlist.add(info);
    info = new Info();
    info.setFormId("B0003");
    info.setAmount(new BigDecimal(120));
    billBatchlist.add(info);
    
    List<Info> payVerifyControlList = new ArrayList<>();
    Info info1 = new Info();
    info1.setFormId("PRE0001");
    info1.setAmount(new BigDecimal(110));
    payVerifyControlList.add(info1);
    info1 = new Info();
    info1.setFormId("PRE0002");
    info1.setAmount(new BigDecimal(190));
    payVerifyControlList.add(info1);
    billBatchlist.forEach(a -> {
        System.out.println("BillFormId:" + a.formId + ",Amount:" + a.getAmount());
    });
    payVerifyControlList.forEach(a -> {
        System.out.println("PreFormId:" + a.formId + ",Amount:" + a.getAmount());
    });
    System.out.println("==================================");
    
    int i = 0, j = 0;
    BigDecimal preAmount = new BigDecimal(0);
    BigDecimal billAmount = new BigDecimal(0);
    while (i < billBatchlist.size() && j < payVerifyControlList.size()) {
        if (preAmount.compareTo(BigDecimal.ZERO) == 0) {
            preAmount = billBatchlist.get(i).amount;
        }
        if (billAmount.compareTo(BigDecimal.ZERO) == 0) {
            billAmount = payVerifyControlList.get(j).amount;
        }
    
        //当前核销金额
        BigDecimal verifyAmount = new BigDecimal(0);
        if (preAmount.compareTo(billAmount) > -1) {
            verifyAmount = billAmount;
            // pre剩余
            preAmount = preAmount.subtract(verifyAmount);
            billAmount = new BigDecimal(0);
        } else {
            verifyAmount = preAmount;
            // bill剩余
            billAmount = billAmount.subtract(verifyAmount);
            preAmount = new BigDecimal(0);
        }
    
        System.out.println("当前核销金额：" + verifyAmount + ",preAmount剩余:" + preAmount + ",billAmount剩余:" + billAmount);
        //大于等于0
        if (preAmount.compareTo(BigDecimal.ZERO) == 0) {
            i++;
        }
        if (billAmount.compareTo(BigDecimal.ZERO) == 0) {
            j++;
        }
    }
    }

打印结果：

BillFormId:B0001,Amount:100
BillFormId:B0002,Amount:80
BillFormId:B0003,Amount:120
PreFormId:PRE0001,Amount:110
PreFormId:PRE0002,Amount:190
==================================
当前核销金额：100,preAmount剩余:0,billAmount剩余:10
当前核销金额：10,preAmount剩余:70,billAmount剩余:0
当前核销金额：70,preAmount剩余:0,billAmount剩余:120
当前核销金额：120,preAmount剩余:0,billAmount剩余:0