父类和子类的操作

父类

public class Father {

}

 子类

public class Son extends Father{

}

 测试

	public static void main(String[] args) {
		Son s = new Son();
		Father f = new Father();
		f =s;//正确
		s = f;//错误 s=(Son)f
                Father f = new Son();//正确
                Son s = new Father();//错误
	}