Java Calendar工作日计算的代码重构与性能提升

在Java中计算工作日可以使用Calendar类来实现，下面是一个简单的实现代码：

import java.util.Calendar;

public class WorkdayCalculator {
  
  public static int calculateWorkdays(Calendar startDate, Calendar endDate) {
    int workdays = 0;
    
    while (startDate.before(endDate)) {
      if (startDate.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY && startDate.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY) {
        workdays++;
      }
      
      startDate.add(Calendar.DAY_OF_MONTH, 1);
    }
    
    return workdays;
  }
  
  public static void main(String[] args) {
    Calendar startDate = Calendar.getInstance();
    Calendar endDate = Calendar.getInstance();
    endDate.add(Calendar.MONTH, 1);
    
    int workdays = calculateWorkdays(startDate, endDate);
    
    System.out.println("Workdays between " + startDate.getTime() + " and " + endDate.getTime() + ": " + workdays);
  }
}

此代码通过循环遍历日期范围内的每一天，如果不是周末则计算为工作日。然而，这种实现方式可能不够高效，特别是在处理大日期范围时。

为了提高性能，可以采用以下方式重构代码：

import java.util.Calendar;

public class WorkdayCalculator {
  
  public static int calculateWorkdays(Calendar startDate, Calendar endDate) {
    int workdays = 0;
    
    while (startDate.before(endDate)) {
      int dayOfWeek = startDate.get(Calendar.DAY_OF_WEEK);
      if (dayOfWeek != Calendar.SATURDAY && dayOfWeek != Calendar.SUNDAY) {
        workdays++;
      }
      
      startDate.add(Calendar.DAY_OF_MONTH, 1);
    }
    
    return workdays;
  }
  
  public static void main(String[] args) {
    Calendar startDate = Calendar.getInstance();
    Calendar endDate = Calendar.getInstance();
    endDate.add(Calendar.MONTH, 1);
    
    int workdays = calculateWorkdays(startDate, endDate);
    
    System.out.println("Workdays between " + startDate.getTime() + " and " + endDate.getTime() + ": " + workdays);
  }
}

在重构代码中，将获取每日的星期几的代码提到循环外部，避免在循环内重复调用。这样可以提高性能，特别是在处理大日期范围时。

另外，可以使用Java 8的新日期时间API（java.time包）来计算工作日，这是一个更加现代化和功能强大的API。