查看了在线截取的代码
public Collection<? extends GrantedAuthority> getAuthorities(Integer role) {
List<GrantedAuthority> authList = getGrantedAuthorities(getRoles(role));
return authList;
}
A.谁能告诉我 ? 是什么意思吗？表示什么？
B. <? extends GrantedAuthority>哪个类正在扩展 GrantedAuthority？
C.在泛型中，我们在<>中提供类类型以确保类型安全，为什么有人想在<>中提供A扩展B？
最佳答案
它是一个通配符，表示任何扩展对象的类型(也包括对象)。
所以你可以说<?>是 <? extends Object> 的简写
检查Oracle docs for Type Arguments and Wildcards
来自here :
In generic code, the question mark (?), called the wildcard, represents an unknown type. The wildcard can be used in a variety of situations: as the type of a parameter, field, or local variable; sometimes as a return type (though it is better programming practice to be more specific). The wildcard is never used as a type argument for a generic method invocation, a generic class instance creation, or a supertype.
关于java - 的意义？在泛型中，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22709444/