为什么此代码段不会出现Java Tutorials文档中所述的运行时错误？

public class Box {
    private Object object;

    public void set(Object object) { this.object = object; }
    public Object get() { return object; }
}

参考官方Java教程文档和上面的代码片段中的这篇文章,我试图重现运行时错误.我的代码有什么问题,因为它没有产生任何运行时错误？

Since its methods accept or return an Object,you are free to pass in whatever you want,provided that it is not one of the primitive types. There is no way to verify,at compile time,how the class is used. One part of the code may place an Integer in the box and expect to get Integers out of it,while another part of the code may mistakenly pass in a String,resulting in a runtime error.

我写的代码.

public class Box {
    private Object obj;

    public void set(Object obj) {
        this.obj = obj;
    }
    public Object get() {
        return obj;
    }

    public static void main(String [] args) {
        Box g = new Box();
        System.out.println(g.get());
        g.set("hello again");
        System.out.println(g.get());
    }
}