Try this:

public static void getMeListOfObjs(List<? extends Object> al) {
    System.out.println(al.get(0));
}

public static void main(String[] args) {

    List<String> al = new ArrayList<String>();

    String mys1 = "jon";

    al.add(mys1);

    getMeListOfObjs(al);


}

This wont compile, because List<String> isn't match List<Object>

As @darijan pointed out the wildcard ? extends the type chack with all class that is descendant of it.

I recommend to read more about generics and wildcards

The code you provided works. I guess you want your al list to be List<String>. Then, you would have to make getMeListOfObjs like this:

public static void getMeListOfObjs(List<? extends Object> al) {
    System.out.println(al.get(0));
}

public static void main(String[] args) {
    List<String> al = new ArrayList<String>();
    String mys1 = "jon";
    al.add(mys1);
    getMeListOfObjs(al);
}

Notice the differnce?

public static void getMeListOfObjs(List<? extends Object> al) {

The wildcard ? changes any type that extends Object, i.e. any object.

您创建的示例不会创建List<String>. 您还可以使用List<Object>您只需将字符串添加到对象列表中。所以你基本上传递了对象列表，这就是它起作用的原因。您可以在对象列表中添加任何对象，包括字符串。它可以工作，因为字符串扩展了对象。

You are passing a List<Object> only. If your concern is that you have passed a String in the List<Object> that is perfectly fine because String IS-A Object.

Because even if you are putting a String as an element in the List<Object>, you are passing a List<Object> to the method.

The book is saying that you can do this:

List al = new ArrayList<String>();

(but Eclipse suggest you not to use raw types... "List is a raw type. References to generic type List should be parameterized")

but you can't do this:

List<Object> al = new ArrayList<String>();

because the compiler recognizes a type mismatch "cannot convert from ArrayList<String> to List<Object>"