书中的例题

				  /*  if-else-if 结构. */
				    class Example2_9 { 
				       public static void main(String args[]) { 
				         int month = 4; // 4月份 
				         String season; 
				         if(month == 12 || month == 1 || month == 2) 
						   {season = "冬天";}
				         else if(month == 3 || month == 4 || month == 5) 
						   {season = "春天"; }
				         else if(month == 6 || month == 7 || month == 8) 
						   {season = "夏天"; }
				         else if(month == 9 || month == 10 || month == 11) 
						   {season = "秋天"; }
				         else 
				           { season = "不合法的月份"; }
				         System.out.println("4月是 " + season + "."); 
				       } 
				    }