受保护构造函数的实际用途是什么?

What are practical uses of a protected constructor?(受保护构造函数的实际用途是什么?)

问题描述

为什么有人会声明构造函数受保护?我知道构造函数被声明为私有是为了不允许它们在堆栈上创建.

Why would anyone declare a constructor protected? I know that constructors are declared private for the purpose of not allowing their creation on stack.

推荐答案

当一个类是(打算作为)抽象类时，受保护的构造函数是完全正确的.在那种情况下，您不希望从类中实例化对象，而只使用它来继承.

When a class is (intended as) an abstract class, a protected constructor is exactly right. In that situation you don't want objects to be instantiated from the class but only use it to inherit from.

还有其他用例，比如当一组特定的构造参数应该限制在派生类时.

There are other uses cases, like when a certain set of construction parameters should be limited to derived classes.

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