public static <T> void show1(List<T> list){
 for (Object object : list) {
        System.out.println(object.toString());
    }
}

public static void show2(List<?> list) {
    for (Object object : list) {
        System.out.println(object);
    }
}

第一种中<T>限制了list中只能放一种类型
第二种中通配符？，list可以add多种类型

https://blog.csdn.net/woshizisezise/article/details/79374460