Question

我正在尝试重构下面的代码，该代码使用多个嵌套的if语句来检查两个列表是否包含相同的项。

List<Car> CarList = CarService.findCarByConfigtype(pageName);
for (int i = 0; i < CarList.size(); i++) {
    System.out.println(CarRestApiController.data().getModel());
    if (CarList.get(i).getModel().equals(CarRestApiController.data().getModel())) {
        dataFound.add(CarList.get(i).getModel());
        if (CarList.get(i).getDerivative().equals(CarRestApiController.data().getDerivative())) {
            dataFound.add(CarList.get(i).getDerivative());
            if (CarList.get(i).getSvp().equals(CarRestApiController.data().getSvp())) {
                dataFound.add(CarList.get(i).getSvp());
                if (CarList.get(i).getEngine().equals(CarRestApiController.data().getEngine())) {
                    dataFound.add(CarList.get(i).getEngine());
                    if (CarList.get(i).getFueltype().equals(CarRestApiController.data().getFueltype())) {
                        dataFound.add(CarList.get(i).getFueltype());
                        if (CarList.get(i).getBodystyle().equals(CarRestApiController.data().getBodystyle())) {
                            dataFound.add(CarList.get(i).getBodystyle());
                            if (CarList.get(i).getTransmission().equals(CarRestApiController.data().getTransmission())) {
                                dataFound.add(CarList.get(i).getTransmission());
                                if (CarList.get(i).getSalescategory().equals(CarRestApiController.data().getSalescategory())) {
                                    dataFound.add(CarList.get(i).getSalescategory());
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

Answer 1

一个解决方案可能是使用Strategy design pattern。为每个if语句制定一个策略，遍历策略列表并处理列表中的每辆车

public interface CarFeatureStrategy {

    boolean canProcess(Car carToProcess, Car carToMatch);

    Object process(Car carToProcess);
}

canHandle方法应封装if语句，该语句必须为true才能进行处理，而process方法应返回汽车相应属性的值（例如此处的示例中的示例）应该是8个策略）

public class ModelStrategy implements CarFeatureStrategy {

    @Override
    public boolean canProcess(Car carToProcess, Car carToMatch) {
        return carToProcess.getModel().equals(carToMatch.getModel));
    }

    @Override
    public Object process(Car carToProcess) {
        return carToProcess.getModel();
    }
}

public class DerivativeStrategy implements CarFeatureStrategy {

    @Override
    public boolean canProcess(Car carToProcess, Car carToMatch) {
        return carToProcess.getModel().equals(carToMatch.getModel())
                && carToProcess.getDerivative().equals(carToMatch.getDerivative());
    }

    @Override
    public Object process(Car carToProcess) {
        return carToProcess.getDerivative();
    }
}

public class SvpStrategy implements CarFeatureStrategy {

    @Override
    public boolean canProcess(Car carToProcess, Car carToMatch) {
        return carToProcess.getModel().equals(carToMatch.getModel())
                && carToProcess.getDerivative().equals(carToMatch.getDerivative())
                && carToProcess.getSvp().equals(carToMatch.getSvp());
    }

    @Override
    public Object process(Car carToProcess) {
        return carToProcess.getSvp();
    }
}

// .... and so on for each condition which needs to be met
// EngineStrategy, FueltypeStrategy, BodystyleStrategy,
// TransmissionStrategy, SalescategoryStrategy

CarProcessor检索与给定pageName对应的汽车，从CarRestApiController检索数据，并使用策略列表来处理汽车

public class CarProcessor {


    private CarService carService;
    private CarRestApiController restController;

    private List<CarFeatureStrategy> carFeatureStrategies;

    public void processCars(Object pageName) {
        // for example purpose the list of strategies is initialized here,
        // but it should be initialized somwhere where the initialization is done
        // only once rather than each time the processCars method is called
        carFeatureStrategies = new ArrayList<>();
        carFeatureStrategies.add(new ModelStrategy());
        carFeatureStrategies.add(new DerivativeStrategy());
        carFeatureStrategies.add(new SvpStrategy());
        // ....
        // add to the strategies list an instance of each strategy to process 
        // the car

        Car carToMatch = restController.data();
        List<Car> cars = carService.findCarByConfigtype(pageName);
        List<Object> dataFound = new ArrayList<>();

        for (Car carToProcess : cars) {
            for (CarFeatureStrategy carFeatureStrategy : carFeatureStrategies) {
                if (carFeatureStrategy.canProcess(carToProcess, carToMatch)) {
                    dataFound.add(carFeatureStrategy.process(carToProcess));
                }
            }
        }
    }
}

可以通过实现Chain of responsibility design pattern对示例进行优化。有了责任链，canHandle方法中的if语句将简化为每个策略一个布尔条件。

对于责任链，必须通过一种方法来增强策略，以返回链中的下一个策略

public interface CarFeatureStrategy {

    boolean canProcess(Car carToProcess, Car carToMatch);

    Object process(Car carToProcess);

    CarFeatureStrategy next();
}

必须参考链中的下一个策略来增强策略的实现

public class ModelStrategy implements CarFeatureStrategy {

    private CarFeatureStrategy nextStrategy;

    public ModelStrategy(CarFeatureStrategy nextStrategy) {
        this.nextStrategy = nextStrategy;
    }

    @Override
    public boolean canProcess(Car carToProcess, Car carToMatch) {
        // check only the model
        return carToProcess.getModel().equals(carToMatch.getModel));
    }

    @Override
    public Object process(Car carToProcess) {
        return carToProcess.getModel();
    }

    @Override
    public CarFeatureStrategy next() {
        return this.nextStrategy;
    }
}

public class DerivativeStrategy implements CarFeatureStrategy {

    private CarFeatureStrategy nextStrategy;

    public DerivativeStrategy(CarFeatureStrategy nextStrategy) {
        this.nextStrategy = nextStrategy;
    }

    @Override
    public boolean canProcess(Car carToProcess, Car carToMatch) {
        // check only the derivative property
        return carToProcess.getDerivative().equals(carToMatch.getDerivative());
    }

    @Override
    public Object process(Car carToProcess) {
        return carToProcess.getDerivative();
    }

    @Override
    public CarFeatureStrategy next() {
        return this.nextStrategy;
    }
}

// ... and so on for all the strategies

CarProcessor应该建立策略链并处理每辆车，直到完成该链（当前策略的next方法返回空值）或当前策略无法处理当前车（{{ 1}}当前策略的方法返回false）

canHandle

Answer 2

我首先按照@ T.J.Crowder的建议将CarList.get(i)和CarRestApiController.data()的结果保存到变量中。然后，我将翻转if-checks并使用continue摆脱嵌套。像这样：

List<Car> carList = CarService.findCarByConfigtype(pageName);

for (int i = 0; i < carList.size(); i++) {
     Car apiData = CarRestApiController.data();
     Car carListData = carList.get(i);

     System.out.println(CarRestApiController.data().getModel());

     if (!carListData.getModel().equals(apiData.getModel())) {
         continue;
     }
     dataFound.add(carListData.getModel());

     if (!carListData.getDerivative().equals(apiData.getDerivative())) {
         continue;
     }
     dataFound.add(carListData.getDerivative());

     if (!carListData.getSvp().equals(apiData.getSvp())) {
         continue;
     }
     dataFound.add(carListData.getSvp());

     // ... and so on.
 }

实现嵌套if语句的另一种方法

2 个答案: