多态的类型转换

class Father
{
	public void say()
	{
		System.out.println("you are so great!");
	}
}
public class ClassCastTest extends Father
{
	public static void main(String[] args) {
		Father f = new ClassCastTest();
		/**
		 * 下面注释的这行代码会出现一个 编译时error
		 * error: incompatible types: Father cannot be converted to ClassCastTest
		 *
		 * Reason: f编译时是Father类型，然后将一个Father类型的f赋予
		 * ClassCastTest类型的cct, 显示是不和适宜的
		 */
		// ClassCastTest cct = f;

		ClassCastTest cct = (ClassCastTest)f;
		cct.say();
	}

	public void say()
	{
		System.out.println("hey girl!");
	}
}