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visibility的背景下,私有和受保护是有意义的,而不是严格意义上的安全功能.
原文链接：https://www.f2er.com/php/139157.htmlClass members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inherited and parent classes. Members declared as private may only be accessed by the class that defines the member.
