为什么不可能重写静态方法?
如果可能,请举例说明。
为什么不可能重写静态方法?
如果可能,请举例说明。
当前回答
一般来说,允许“重写”静态方法是没有意义的,因为没有好的方法来确定在运行时调用哪个方法。以Employee为例,如果我们调用regularemploee . getbonusmultiplier()——应该执行哪个方法?
以Java为例,人们可以想象这样一种语言定义:只要静态方法是通过对象实例调用的,就可以“覆盖”它们。然而,这样做只是重新实现常规的类方法,在没有真正带来任何好处的情况下为语言增加冗余。
其他回答
I like and double Jay's comment (https://stackoverflow.com/a/2223803/1517187). I agree that this is the bad design of Java. Many other languages support overriding static methods, as we see in previous comments. I feel Jay has also come to Java from Delphi like me. Delphi (Object Pascal) was one of the languages implementing OOP before Java and one of the first languages used for commercial application development. It is obvious that many people had experience with that language since it was in the past the only language to write commercial GUI products. And - yes, we could in Delphi override static methods. Actually, static methods in Delphi are called "class methods", while Delphi had the different concept of "Delphi static methods" which were methods with early binding. To override methods you had to use late binding, declare "virtual" directive. So it was very convenient and intuitive and I would expect this in Java.
重写是为实例成员保留的,以支持多态行为。静态类成员不属于特定实例。相反,静态成员属于类,因此不支持重写,因为子类只继承受保护和公共实例成员,而不继承静态成员。您可能希望定义一个接口,并研究工厂和/或策略设计模式,以评估替代方法。
Here is a simple explanation. A static method is associated with a class while an instance method is associated with a particular object. Overrides allow calling the different implementation of the overridden methods associated with the particular object. So it is counter-intuitive to override static method which is not even associated with objects but the class itself in the first place. So static methods cannot be overridden based on what object is calling it, it will always be associated with the class where it was created.
一般来说,允许“重写”静态方法是没有意义的,因为没有好的方法来确定在运行时调用哪个方法。以Employee为例,如果我们调用regularemploee . getbonusmultiplier()——应该执行哪个方法?
以Java为例,人们可以想象这样一种语言定义:只要静态方法是通过对象实例调用的,就可以“覆盖”它们。然而,这样做只是重新实现常规的类方法,在没有真正带来任何好处的情况下为语言增加冗余。
重写依赖于类的实例。多态性的意义在于,您可以子类化一个类,而实现这些子类的对象对于父类中定义的相同方法将具有不同的行为(并且在子类中被重写)。静态方法不与类的任何实例相关联,因此这个概念不适用。
There were two considerations driving Java's design that impacted this. One was a concern with performance: there had been a lot of criticism of Smalltalk about it being too slow (garbage collection and polymorphic calls being part of that) and Java's creators were determined to avoid that. Another was the decision that the target audience for Java was C++ developers. Making static methods work the way they do had the benefit of familiarity for C++ programmers and was also very fast, because there's no need to wait until runtime to figure out which method to call.