何时使用静态方法 [英] When to use static methods

问题描述

我想知道什么时候使用静态方法?假设我有一个带有一些 getter 和 setter 的类、一两个方法，并且我希望这些方法只能在类的实例对象上调用.这是否意味着我应该使用静态方法?

I am wondering when to use static methods? Say if I have a class with a few getters and setters, a method or two, and I want those methods only to be invokable on an instance object of the class. Does this mean I should use a static method?

示例:

Obj x = new Obj();
x.someMethod();

...或:

Obj.someMethod(); // Is this the static way?

我有点困惑！

推荐答案

一个经验法则:问问自己即使尚未构造任何对象，调用此方法是否有意义?";如果是这样，它肯定应该是静态的.

One rule-of-thumb: ask yourself "Does it make sense to call this method, even if no object has been constructed yet?" If so, it should definitely be static.

所以在 Car 类中你可能有一个方法:

So in a class Car you might have a method:

double convertMpgToKpl(double mpg)

...这将是静态的，因为人们可能想知道 35mpg 转换成什么，即使没有人制造过 Car.但是这个方法(它设置了一个特定Car的效率):

...which would be static, because one might want to know what 35mpg converts to, even if nobody has ever built a Car. But this method (which sets the efficiency of one particular Car):

void setMileage(double mpg)

...不能是静态的，因为在构造任何 Car 之前调用该方法是不可思议的.

...can't be static since it's inconceivable to call the method before any Car has been constructed.

(顺便说一句，反过来并不总是正确的:您有时可能有一个涉及两个 Car 对象的方法，并且仍然希望它是静态的.例如:

(By the way, the converse isn't always true: you might sometimes have a method which involves two Car objects, and still want it to be static. E.g.:

Car theMoreEfficientOf(Car c1, Car c2)

虽然这可以转换为非静态版本，但有些人会争辩说，因为没有特权"版本.选择哪个 Car 更重要，你不应该强迫调用者选择一个 Car 作为你调用方法的对象.不过，这种情况只占所有静态方法的一小部分.

Although this could be converted to a non-static version, some would argue that since there isn't a "privileged" choice of which Car is more important, you shouldn't force a caller to choose one Car as the object you'll invoke the method on. This situation accounts for a fairly small fraction of all static methods, though.

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