父類：
package?cn.edu.aufe.demol2;

public?class?Animal?{
	public?void?eat(){
		System.out.println("動物具有吃的能力");
	}
}
子類：
package?cn.edu.aufe.demol2;

import?cn.edu.aufe.demol.Animal;

public?class?Dog?extends?Animal?{
	public?void?eat(){
		System.out.println("狗具有吃的能力");
	}
}
main()函數：
package?cn.edu.aufe.demol2;

public?class?Initial?{


	public?static?void?main(String[]?args)?{
		//?TODO?Auto-generated?method?stub
		
		Animal?obj1=new?Animal();
		Animal?obj2=new?Dog();
		
	}

}

但是在編寫Animal obj2=new Dog()的時候，編譯器總是報錯，讓我把寫成Dog obj2=new Dog();但我認為我寫的沒錯啊