利用Java怎么获取指定的时间

package getBeforeHourDemo;
import java.text.SimpleDateFormat;
import java.util.Calendar;
//获取当前时间，指定前面多少小时的时间 
//返回格式YYYYMMDDHHMMSS 
public class getBeforeHourTime {
  public static String getBeforeByHourTime(int ihour){ 
     String returnstr = ""; 
     Calendar calendar = Calendar.getInstance(); 
     calendar.set(Calendar.HOUR_OF_DAY, calendar.get(Calendar.HOUR_OF_DAY) - ihour); 
     SimpleDateFormat df = new SimpleDateFormat("yyyyMMddHHmmss"); 
     returnstr = df.format(calendar.getTime()); 
     return returnstr; 
  } 
  public static void main(String[] args) {
    String beforetime=getBeforeByHourTime(2);
    System.out.println(beforetime); 
  }
}