将当前行与前一行进行比较爪哇

如何解决将当前行与前一行进行比较爪哇

我想将当前行与前一行进行比较，如果匹配，则进行计算。如果不是，则赋值 0.0 我的代码只计算不接受条件。

例如我有表：油 油由月份、日期和指示器组成

它必须看起来像：

Month      Values  Date        |formula              |Growth
september   100     01.09.2020  |(100/nan - 1) * 100  |infinity
september   80      08.09.2020  |(80/100-1) * 100     |-20
september   100     15.09.2020  |(100/80-1) * 100     |25     
october     118     01.10.2020  |september != october |0
october     120     08.10.2020  |(120/118-1) * 100    |1.69                 
october     123     15.10.2020  |(123/120-1) * 100    |2.5
november    122     01.11.2020  |october != november  |0
november    122     08.11.2020  |(122/122-1) * 100    |0                    

我的班级模型：

@Entity
@Table(name = "oper_mon_oil_price")

public class OilModel {

@Id
@GeneratedValue(strategy =  GenerationType.IDENTITY)
private long id;
@Column(name = "o_year")
private String oyear;
@Column(name = "o_month")
private String omonth;
@Column(name = "o_date_event")
private String odateEvent;
@Column(name = "o_period")
private String operiod;
@Column(name = "o_area")
private String oarea;
@Column(name = "o_unit")
private String ounit;
@Column(name = "o_ai_92")
public Double oai92;
@Column(name = "o_ai_95")
public Double oai95;
@Column(name = "o_diesel_winter")
private Double odieselWinter;
@Column(name = "o_diesel_fuel_offseason")
private Double odieselFuelOffseason;
@Column(name = "growth_ai_92")
public Double growthAi92;
@Column(name = "growth_ai_95")
public Double growthAi95;
@Column(name = "growth_diesel_winter")
public Double growthDieselWinter;
@Column(name = "growth_diesel_fuel_offseason")
public Double growthDieselFuelOffseason;
 
getters/setters
}

类库：

@Repository
@Mapper
public interface OilProdTovRepo {

@Select("SELECT * FROM oper_mon_prod_tov ORDER BY o_year ASC,o_month ASC,o_date_event ASC ")
@Results(value ={
        @Result(property = "id",column = "id"),@Result(property = "area",column = "o_area"),@Result(property = "year",column = "o_year"),@Result(property = "month",column = "o_month"),@Result(property = "period",column = "o_period"),@Result(property = "dateEvent",column = "o_date_event"),@Result(property = "unit",column = "o_unit"),@Result(property = "wheatFlourFirstGrade",column = "o_wheat_flour_first_grade"),@Result(property = "wheatBread",column = "o_wheat_bread"),@Result(property = "horns",column = "o_horns"),@Result(property = "buckwheat",column = "o_buckwheat"),@Result(property = "polishedRice",column = "o_polished_rice"),@Result(property = "potato",column = "o_potato"),@Result(property = "carrots",column = "o_carrots"),@Result(property = "onion",column = "o_onion"),@Result(property = "cabbageWhite",column = "o_cabbage_white"),@Result(property = "sugar",column = "o_sugar"),@Result(property = "oil",column = "o_oil"),@Result(property = "beef",column = "o_beef"),@Result(property = "chickenMeat",column = "o_chicken_meat"),@Result(property = "milk",column = "o_milk"),@Result(property = "kefir",column = "o_kefir"),@Result(property = "butter",column = "o_butter"),@Result(property = "egg",column = "o_egg"),@Result(property = "salt",column = "o_salt"),@Result(property = "cottageCheese",column = "o_cottage_cheese"),@Result(property = "growthWheatFlourFirstGrade",column = "o_growth_wheat_flour_first_grade"),})
List<OilProdTovModel> getoilProdTovModel();

@Update("UPDATE oper_mon_prod_tov SET o_growth_wheat_flour_first_grade=#{growthWheatFlourFirstGrade} WHERE id=#{id}")
void updateWheatFlourFirstGrade(OilProdTovModel oilProdTovModel);
}

还有主类 Service :

@Service
public class OilProdTovService {
@Autowired
public OilProdTovRepo oilProdTovRepo;

public List<OilProdTovModel> allOilProdTov() {
    List<OilProdTovModel> oilProdTovModels = oilProdTovRepo.getoilProdTovModel();
    Double first = 0.0;
    Double result;
    for (OilProdTovModel oilProdTovModel : oilProdTovModels) {
        if (oilProdTovModel.getMonth().equals("September")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        } else if (oilProdTovModel.getMonth().equals("October")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        }
        else if (oilProdTovModel.getMonth().equals("November")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        }
        else {
            oilProdTovModel.setGrowthWheatFlourFirstGrade(0.0);
        }
        
        oilProdTovRepo.updateWheatFlourFirstGrade(oilProdTovModel);
    }
    return oilProdTovRepo.getoilProdTovModel();
}
}

如何修改我的代码？

解决方法

由于您似乎很难在列表中找到 2 个相互跟随的实体，因此您可以这样做：

使用“foreach”：

List<OilProdTovModel> oilProdTovModels = ...
OilProdTovModel prev = null;
for (OilProdTovModel oilProdTovModel : oilProdTovModels) {
  if( prev != null ) {
    //compare oilProdTovModel and prev here
  }

  prev = oilProdTovModel; //keep track of the current element to serve as prev for the next iteration
}

使用传统的 for 循环：

for (int i = 1; i < oilProdTovModels.size(); i++) {
  OilProdTovModel prev = oilProdTovModels.get(i - 1);
  OilProdTovModel current = oilProdTovModels.get(i);

  //compare both - if you need to handle the first element without any comparison then do that before the loop 
  //(or iterate from 0 to size() - 1 and handle the last element after the loop if needed)
}