Java的默认访问修饰符曾经是公开的

早在2004年,当我在RIT参加CS课程的介绍时,我的教授非常强调我们记得放入访问修饰语.没有它,默认访问将是公开的,我记得教授说的.也许我的记忆是错的,教授实际上并没有说出来,但显然现在情况并非如此.我想知道在某些时候是否曾经是这种情况,也许Sun在2004年之后的某些时候改变了它？

解决方法:

自Java 1.0以来,没有访问修饰符的Java类一直是包私有的.

以下是JLS 1.0适用部分的链接：

If a class or interface type is declared public, then it may be accessed by any Java code that can access the package in which it is declared. If a class or interface type is not declared public, then it may be accessed only from within the package in which it is declared.

对于类型内的成员,它说：

A member (field or method) of a reference (class, interface, or array)
type or a constructor of a class type is accessible only if the type
is accessible and the member or constructor is declared to permit
access:

• If the member or constructor is declared public, then access is
  permitted. All members of interfaces are implicitly public.

• Otherwise, if the member or constructor is declared protected, then
  access is permitted only when one of the following is true:

  • Access to the member or constructor occurs from within the package containing the class in which the protected member is
    declared.
  • Access occurs within a subclass of the class in which the protected member is declared, and the access is correct as described
    in §6.6.2.

• Otherwise, if the member or constructor is declared
  private, then access is permitted only when it occurs from within the
  class in which it is declared.

• Otherwise, we say there is default
  access, which is permitted only when the access occurs from within the
  package in which the type is declared.

这意味着如果没有修饰符,类的成员/构造函数将是包私有的,而不是公共的.

但是,接口的成员绝不是公共的,所以对它们应用访问修饰符不会改变一个东西(好吧,如果你尝试私有或受保护,你会得到一个编译错误),所以无论你怎么记得教授说,它不适用于接口.

标签：java,access-modifiers
来源： https://codeday.me/bug/20190724/1526998.html