ex0509.java

JAVA的一些例子,大家可以参考一下

		//
		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;   //自动类型转换
			}
		}
		//以下两种写法均出错
		b y;				b y;
		a x = new a();			a x = new b();
		y = x;				y = x;
		//编译通过，运行时异常
		b y;				
		a x = new a();			
		y = (b) x;		
		//以下编译运行均正常
		b y;				
		a x = new b();			
		y = (b)x;