BigDecimal的用法

1.例子
public class Test {
 public static void main(String[] args) {
  BigDecimal big1 = new BigDecimal("600");
  BigDecimal big2 = new BigDecimal("300");
  //两个BigDecimal相加
  big1 = big1.add(big2);
  System.out.println(big1);
  //两个BigDecimal相减
  big1 = big1.subtract(big2);
  System.out.println(big1);
  //两个BigDecimal相乘
  big1 = big1.multiply(big2);
  System.out.println(big1);
  //两个BigDecimal相除
  big1 = big1.divide(big2);
  System.out.println(big1);
  //如果是Long 型
  BigDecimal big3 = BigDecimal.valueOf(200L);   big1 = big1.subtract(big3);   System.out.println("big1=" + big1);
  
 }
}
//输出效果


2.项目中的应用
/**
  * 1.降要删除的数据的paymentSummaryid设为null ;
  * 2.总金额相减
  *
  * @param paymentId
  */
 public void setPaymentSummaryIdNull(Long paymentId, Long paymentSummaryId) {
  Payment payment = payMentRepository.findOne(paymentId);
  PaymentSummary summary = paymentSummaryRepository.findOne(78456137l);


  int count = findPaymentSummaryIdList(paymentSummaryId).size();//总数
  List resultList = findPaymentSummaryIdList(paymentSummaryId);
  if (count != 0) {
   for (int i = 0; i < count; i++) {
    if (resultList.get(i) == paymentId) {  //如果list里的ID等于paymentId总数相减
     PaymentSummary paymentSummary =            paymentSummaryRepository.findOne(paymentSummaryId);
     //paymentSummary.getSummaryFee()是BigDecimal类型，（paymentSummary是实体）
     //必须得先把paymentSummary.getSummaryFee()转换成String 在转成Double
     BigDecimal summaryFee = new BigDecimal
       (Double.valueOf(paymentSummary.getSummaryFee().toString())); //得到总金额
     BigDecimal paymentFee = new BigDecimal
       (Double.valueOf(payment.getFee().toString())); //得到要修改的数据的费用
     paymentSummary.setSummaryFee(summaryFee.subtract(paymentFee));//两个值相减
     paymentSummary = paymentSummaryRepository.save(paymentSummary);
    }
   }
  }




  payment.getFee();
  payment.setPaymentSummary(summary);
  payment = payMentRepository.save(payment);


 }