Java中的继承多态性和动态绑定

Question

我有一个子类Host，它扩展了超类User

public abstract class User
{
    public String user_name;
    public String toString()
    {
        return this.getClass() + " Name: " + this.user_name;
    }
}

class Host extends User
{
    public Host(String user_name)
    {
        this.user_name=user_name;
    }
    public void test()
    {
        System.out.println(user_name + " pass");
    }
}

内主（）

    User _host1 = new Host("h1");
    Host _host2 = new Host("h2");
    System.out.println(_host1);  //class Host Name: h1
    System.out.println(_host2);  //class Host Name: h2
    _host1.test();   //this gives me an error
    _host2.test();   //this is fine

我确信_host1和_host2都属于Host类

我不明白的是，为什么通过动态绑定创建的_host1无法访问类Host内的方法test()

我错过了什么