在调用类似的类Java时去掉if/else

Question

我有我想要的问题,需要摆脱一些if else案例.我在我的项目中得到以下代码:

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());
}

这三个类WeekThreshold,MonthThreshold并YearThreshold从AbstractThreshold他们从日历中获取日期的类延伸,但这并不重要.方法quarterThreshold()很特别,可以留在那里.但是,我怎样才能摆脱那个if else块并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]是月份,则MonthThreshold必须调用等.

Answer 1

这里可以很好的利用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;
  }
}

其余代码如下所示：

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