受保护成员的范围 [英] Scope of protected members

问题描述

Iam准备SCJP，我也知道受保护的成员范围在包内以及其他包中，只有继承可能有一些条件。

Iam preparing for SCJP , also i came to know that protected members scope is within the package as well as in other package with some conditions like possible only with inheritance.

例如：
i有三个类作为Parentclass Childclass Friendclass

For example : i have three classes as Parentclass Childclass Friendclass

package x.parent;

 class Parentclass{
 protected int x=10;
  ...............
  }

 package x.child;

 class Childlass extends Parentclass{
  super.x=20;
  ...............
}

 package x.child;

 import x.parent.Parentclass;

 class Friendclass{
 Parentclass pc = new Parentclass();
 pc.x=30;
  ...............
}

背后的原因是，在Friendclass中，成员x不接受为其分配值，如果是Childclass，则表现为私有成员。

Whats the reason behind that, in Friendclass the member x will not accept to assign a value to that, behaves as private member not in case of Childclass.

推荐答案

您甚至无法访问 Childclass 中的 Parentclass.x ，因为 x 具有默认可见性（未受保护）。请参阅 http://download.oracle.com/javase/tutorial/java/ javaOO / accesscontrol.html

You can't even access Parentclass.x in Childclass because x has default visibility (not protected). See http://download.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html

编辑：

x.child .Friendclass 与 x.parent.Parentclass 不在同一个包中。
x.child.Friendclass 不从 x.parent.Parentclass继承 。

x.child.Friendclass is not in the same package as x.parent.Parentclass. x.child.Friendclass does not inherit from x.parent.Parentclass.

作为TotalFrickinRockstarFromMars的摘要状态和Java访问控制文档也说明，这意味着不允许 Friendclass 访问字段 x 。

as TotalFrickinRockstarFromMars's summary states and the Java access control docs also state, this means that Friendclass is not allowed to access the field x.

这篇关于受保护成员的范围的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！