在Java中使用静态变量的优点 [英] Advantage of using static variables in Java

问题描述

假设我有两个这样的类：

Say I have two classes like this:

class A{  
    private static Random random = new Random();  

    public A(){  
        // Do something.
    }

    public Integer methodGetsCalledQuiteOften(){
        return random.nextInt();
    }
}

class B{  
     private Random random;  

     public A(){  
         random = new Random();
         // Do something.
     }

     public Integer methodGetsCalledQuiteOften(){
         return random.nextInt();
     }
}

在两个实例化多次实例化的情况下并且这两个类的'实例'方法 methodGetsCalledQuiteOften 被大量调用，是否有任何真正的优势/劣势（时间，内存）使用a在A类中保存 Random（）的静态变量，而不是在每个实例中创建一个新的 Random（）对象，就像在B类一样？

In a scenario where both of them get instantiated multiple times and both of these classes' instances' method methodGetsCalledQuiteOften gets called a lot, is there any real advantage/disadvantage (time, memory) in using a static variable that holds Random() in class A as opposed to creating a new Random() object in every single instance, like in class B?

该应用程序是多线程的，随机性水平较高，所以我认为我将使用静态 SecureRandom 。如果在分析后这将是一个真正的速度因素，我可能会选择其他东西。

The application is multithreaded and higher level of randomness is so I think I am going with static SecureRandom. If that will be a real speed factor after profiling I might choose something else.

推荐答案

真正的优势/缺点取决于真正的代码。换句话说，它取决于创建 B 的频率与调用该方法的频率等相比。您应该分析您的应用程序并查看它是否有合理的差异。

Real advantage/disadvantages depend on real code. In other words, it depends on how often a B is created compared to how often the method is called, etc. You should profile your application and see whether it makes a reasonable difference.

A会比B更高效吗？当然。但是，你是否会注意到取决于你的用法。 A会比B使用更少的内存吗？当然，但你是否关心取决于你要保留多少个A / B实例。

Will A be more performant than B? Certainly. But whether you'll ever notice depends on your usage. Will A use less memory than B? Certainly, but whether you care or not depends on how many instances of A/B you're keeping around.

真正唯一的另一个考虑因素是决定论。由于您没有为Random实例指定种子，我认为您不关心是否可以从Random重现数字序列。但是值得注意的是......如果你有一个共享的随机数，那么为某个A实例保证一定数量的确定性数字序列要比在B中每个实例保证一个确定的数字序列要困难得多。

Really the only other consideration is determinism. Since you don't specify the seed for the Random instance, I take it you don't care whether you can reproduce the sequence of numbers from the Random. But it's worth noting...if you have a shared Random, it will be much harder to guarantee a certain deterministic sequence of numbers for some instance of A than it is with one per instance as in B.

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