//
		class a{
			int year = 2003;
		}

		class b extends a{
			int month = 12;
		}
		
		class c extends a{
			int day = 1;
		}

		class Test{
			public static void main(String args[]){
				a x;
				b y; = new b();
				x = y;   //自動類型轉換
			}
		}
		//以下兩種寫法均出錯
		b y;				b y;
		a x = new a();			a x = new b();
		y = x;				y = x;
		//編譯通過，運行時異常
		b y;				
		a x = new a();			
		y = (b) x;		
		//以下編譯運行均正常
		b y;				
		a x = new b();			
		y = (b)x;