我发现静态变量使用起来更方便。而且我认为它们也很有效(如果我错了请纠正我)，因为如果我必须在一个类中对一个函数进行10,000次调用，我很乐意将方法设置为静态的，并在其上使用直接的class. methodcall()，而不是用10,000个类实例来混乱内存，对吗?

我明白你的想法，但一个简单的单例模式将做同样的事情，而不必实例化10,000个对象。

可以使用静态方法，但只能用于与对象域相关且不需要或使用对象的内部属性的函数。

ex:

public class WaterContainer {
    private int size;
    private int brand;
    ...etc

    public static int convertToGallon(int liters)...

    public static int convertToLiters(int gallon)...

}

在我看来，这与性能无关，而是与设计有关。我不认为使用静态方法和使用静态变量是错误的(但我猜你实际上是在谈论方法调用)。

它只是关于如何分离逻辑并给它一个好的位置。有时这证明使用静态方法是正确的，java.lang.Math就是一个很好的例子。我认为，当您将大多数类命名为XxxUtil或Xxxhelper时，您最好重新考虑您的设计。

假设您有一个拥有许多用户的应用程序，并且您已经定义了一个静态函数，该函数将状态保存在一个静态变量中，那么每个用户都将修改其他用户的状态。

静态变量本身并没有什么问题。只是Java语法有问题。每个Java类实际上定义了两个结构——一个封装静态变量的单例对象和一个实例。在同一个源代码块中定义这两种代码是非常糟糕的，会导致代码难以阅读。Scala做得很好。

在你的文章中有两个主要问题。

First, about static variables. Static variables are completelly unnecesary and it's use can be avoided easily. In OOP languajes in general, and in Java particularlly, function parameters are pased by reference, this is to say, if you pass an object to a funciont, you are passing a pointer to the object, so you dont need to define static variables since you can pass a pointer to the object to any scope that needs this information. Even if this implies that yo will fill your memory with pointers, this will not necesary represent a poor performance because actual memory pagging systems are optimized to handle with this, and they will maintain in memory the pages referenced by the pointers you passed to the new scope; usage of static variables may cause the system to load the memory page where they are stored when they need to be accessed (this will happen if the page has not been accesed in a long time). A good practice is to put all that static stuf together in some little "configuration clases", this will ensure the system puts it all in the same memory page.

Second, about static methods. Static methods are not so bad, but they can quickly reduce performance. For example, think about a method that compares two objects of a class and returns a value indicating which of the objects is bigger (tipical comparison method) this method can be static or not, but when invoking it the non static form will be more eficient since it will have to solve only two references (one for each object) face to the three references that will have to solve the static version of the same method (one for the class plus two, one for each object). But as I say, this is not so bad, if we take a look at the Math class, we can find a lot of math functions defined as static methods. This is really more eficient than putting all these methods in the class defining the numbers, because most of them are rarelly used and including all of them in the number class will cause the class to be very complex and consume a lot of resources unnecesarilly.

总之:在处理静态或非静态方法时，避免使用静态变量，并找到正确的性能平衡。

PS:抱歉我的英语不好。

静态变量表示全局状态。这很难推理，也很难测试:如果我创建了一个对象的新实例，我就可以在测试中推理它的新状态。如果我使用使用静态变量的代码，它可以处于任何状态-任何东西都可以修改它。

我还可以继续讲很久，但更重要的概念是，事物的范围越窄，就越容易进行推理。我们擅长思考小事，但如果没有模块化，就很难推断出百万行系统的状态。顺便说一下，这适用于各种各样的东西——不仅仅是静态变量。