JAVA 引用对象时应该用接口类型还是实现类的类型

//implA 为接口  ClassB为其实现类
implA A=new ClassB();  //接口类型的引用变量A 去接收对象地址
or
ClassB A=new ClassB();  //类类型的引用变量A 去接收对象地址

public class InterfaceTest {

    public static void main(String[] args) {
        PetInterface p = new Cat();
        p.talk();
        p.batheSelf();//无法调用 ，报错The method batheSelf() is undefined for the type PetInterface
    }

}

interface PetInterface {                
    public void talk();
}

class Dog implements PetInterface {
    @Override
    public void talk() {
        System.out.println("Bark!");
    }
}

class Cat implements PetInterface {
    @Override
    public void talk() {
        System.out.println("Meow!");
    }
    public void batheSelf() {
        System.out.println("Cat bathing");
    }
}