Question

我有我想要的问题，需要摆脱一些if else案例。我在我的项目中获得了以下代码：

if (ar[4].equals("week")) {

    WeekThreshold wt = new WeekThreshold();
    firstTime = unparsedDate.format(wt.getStartDate().getTime());
    secondTime = unparsedDate.format(wt.getEndDate().getTime());

} else if (ar[4].equals("month")) {

    MonthThreshold mt = new MonthThreshold();
    firstTime = unparsedDate.format(mt.getStartDate().getTime());
    secondTime = unparsedDate.format(mt.getEndDate().getTime());

} else if (ar[4].equals("quarter")) {

    quarterThreshold();

} else if (ar[4].equals("year")) {

    YearThreshold yt = new YearThreshold();
    firstTime = unparsedDate.format(yt.getStartDate().getTime());
    secondTime = unparsedDate.format(yt.getEndDate().getTime());
}

这三个课程WeekThreshold，MonthThreshold和YearThreshold来自AbstractThreshold课程，他们从日历中获取日期，但这并不重要。方法quarterThreshold()很特别，可以留在那里。但是，我怎么能摆脱那个if else块并且有一个语句来调用不同的类？

编辑：忘记提及，需要调用的类来自各种数组ar[]。如果数组ar[4]为月，则必须调用MonthThreshold等

Answer 1

多种可能性...... XYZThreshold类是否具有通用接口，如阈值？然后你可以用它来分配一个变量，例如......

Threshold threshold = null;
if ((ar[4].equals("week")) {
  threshold = new WeekThreshold();
} else ... {

}

firstTime = unparsedDate.format(threshold.getStartDate().getTime());
secondTime = unparsedDate.format(threshold.getEndDate().getTime());

这将是第一步。如果您愿意，您可以使用枚举来存储阈值：

enum Thresholds {
  WEEK("week") {

     public Threshold getThreshold() {
           return new WeekThreshold();
     }
  },
  etc.

  private String period;

  private Thresholds(String period) {
    this.period = period;
  }

  public abstract Threshold getThreshold();

  //  ...add a static class to iterate and search by period, 
  // ...so you can write Threshold threshold = Thresholds.getByPeriod("week").getThreshold();
}

使用枚举是个人品味，当然，您可以使用普通类或仅将阈值选择的if-block放入单独的类中来执行相同的操作。

Answer 2

您可以将公共代码（unparsedDate.format(...)）合并到外面，如下所示：

AbstractThreshold at = null;
switch(ar[4]) {
case "week":
    at = new WeekThreshold();
    break;
case "month":
    at = new MonthThreshold();
    break;
case "year":
    at = new YearThreshold();
    break;
case "quarter":
    quarterThreshold();
    break;
}
if(at != null) {
    firstTime = unparsedDate.format(at.getStartDate().getTime());
    secondTime = unparsedDate.format(at.getEndDate().getTime());
}

当然可以使用过度设计的版本。这里只是说明如何使用Java-8功能实现它：

// Map can be initialized only once, then used many times
Map<String, Supplier<AbstractThreshold>> thresholdSuppliers = new HashMap<>();
thresholdSuppliers.put("week", WeekThreshold::new);
thresholdSuppliers.put("month", MonthThreshold::new);
thresholdSuppliers.put("year", YearThreshold::new);

AbstractThreshold at = thresholdSuppliers.getOrDefault(ar[4], () -> null).get();
if(at != null) {
    firstTime = unparsedDate.format(at.getStartDate().getTime());
    secondTime = unparsedDate.format(at.getEndDate().getTime());
} else if(ar[4].equals("quarter"))
    quarterThreshold();
}

Answer 3

在这里，您可以充分利用FactoryPattern

class ThresholdFactory
{
  public static AbstractThreshold getThreshold(String criteria)
  {
    if ( criteria.equals("week") )
      return new WeekThreshold();
    if ( criteria.equals("month") )
      return new MonthThreshold();
    if ( criteria.equals("year") )
      return new YearThreshold();

    return null;
  }
}

其余的代码看起来像这样：

AbstractThreshold at = ThresholdFactory.getThreshold(ar[4]);
if(at != null){
  firstTime = unparsedDate.format(at.getStartDate().getTime());
  secondTime = unparsedDate.format(at.getEndDate().getTime());
} else {
   quarterThreshold();
}

Answer 4

以下是如何使用接口和工厂设计模式的示例如果您的多个实现者共享公共代码，请让它们都扩展一个实现该接口的Abstract类。通过接口引用您的方法是个好主意，而不是利用多态性的具体类...请参阅下面的代码...

public class Example {

    public static void main(String[] args) {

        String[] intervals = {"week", "week", "quarter", "month", "year", "week"}; 

        IThreshold[] objects = new IThreshold[intervals.length];

        // Create your objects using Factory pattern
        for(int index = 0; index < intervals.length; index++) {
            objects[index] = ThresholdFactory.createInstance(intervals[index]);
        }

        // Now iterate through your objects and refer to them through a common interface
        for(IThreshold object : objects) {
            int start = object.getFirstTime();
            int end = object.getFirstTime();
        }
    }
}

interface IThreshold {
    public int getFirstTime();
    public int getLastTime();
}


abstract class AbstractThreshold implements IThreshold {

    @Override
    public int getFirstTime() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public int getLastTime() {
        // TODO Auto-generated method stub
        return 0;
    }

}

class WeekThreshold extends AbstractThreshold {}
class MonthThreshold extends AbstractThreshold {}
class QuarterThreshold extends AbstractThreshold {}
class YearThreshold extends AbstractThreshold {}

class ThresholdFactory {

    public static final IThreshold createInstance(String interval) {
        IThreshold instance = null;

        if(interval.equals("week")){
            instance = new WeekThreshold();
        } 
        else if(interval.equals("month")){
            instance = new MonthThreshold();
        } 
        else if(interval.equals("quarter")){
            instance = new QuarterThreshold();
        } 
        else {
            if(interval.equals("year")){
                instance = new YearThreshold();
            }
        }
        return instance;
    }
}

Answer 5

首先创建阈值工厂，

static enum ThresholdsFactory {


        week(new WeekThreshold()), month(new MonthThreshold())/* etc */;

        static private Map<String,ThresholdsFactory> lookup = new HashMap<String, ThresholdsFactory>();
        static{
            for(ThresholdsFactory val :  ThresholdsFactory.values()){
            lookup.put(val.name(), val);
            }
        }

        public AbstractThreshold threshold;

        public static ThresholdsFactory find(String name){
            return lookup.get(name);
        }

        ThresholdsFactory(AbstractThreshold th) {
            threshold = th;

} }

现在您需要做的就是

AbstractThreshold th = ThresholdsFactory.find(ar[4]);

if (th!=null){
    firstTime = unparsedDate.format(th.getStartDate().getTime());
    secondTime = unparsedDate.format(th.getEndDate().getTime());
}

Answer 6

您可以使用switch语句

String typeOfDay;
     switch (dayOfWeekArg) {
         case "Monday":
             typeOfDay = "Start of work week";
             break;
         case "Tuesday":
         case "Wednesday":
         case "Thursday":
             typeOfDay = "Midweek";
             break;
         case "Friday":
             typeOfDay = "End of work week";
             break;
         case "Saturday":
         case "Sunday":
             typeOfDay = "Weekend";
             break;
         default:
             throw new IllegalArgumentException("Invalid day of the week: " + dayOfWeekArg);
     }

您可以使用自己的代码替换我从java文档中窃取的示例

switch(periodType){
    case "week":
      WeekThreshold wt = new WeekThreshold();
    break; // add your other cases
}
firstTime = unparsedDate.format(wt.getStartDate().getTime());
secondTime = unparsedDate.format(wt.getEndDate().getTime());

调用类似的类Java

6 个答案: