从类< A>访问静态字段变量 [英] Accessing static field from Class<A> variable

问题描述

我有以下情况（我知道它不是真的，但我简化了它为了更好地理解）：

• A


• 其他类 B，C，D，... 扩展A


• 方法 foo （ classz）;

（其他地方，无关紧要）

现在我想要这个方法实现返回值，如果静态字段 f ，从 classz ; A 的子类可能有不同的值。我不想使用反射（和新的jdk7 invoke。*功能）。现在，我有这个解决方案工作，但不好，因为它instanciates一个对象（这不应该是必要的），并通过访问一个静态字段从一个实例生成警告：

  int foo（Class< A> classz）throws [do not matter] {
 return classz.newInstance（）。 
} 
  

有任何建议吗？
提前感谢？

PS：不知道如何输入 Class< ？> 没有空格...

解决方案

do或为什么你传递一个类 - 它看起来像你应该只需要：

  int foo（）{ 
 return Af; 
} 
  

成功后，这就是你当前的代码将返回。您的代码等效于：

  int foo（Class< A> classz）throws ... {
 = classz.newInstance（）; 
 return A.f; 
} 
  

这听起来像是你多态与静态字段 - 这根本不工作。静态成员不是多态的，也不是字段。如果您在每个子类别中声明额外的 f 字段，您将必须使用反射来获取它们，但我建议您重新设计。如果您不在每个子类中声明额外的 f 字段，则您只有一个字段 - Bf 和 Cf 将基本解析为 Af $ b

I have the following situation (I know it doesn't sound real but I simplified it for better understanding):

• A class A, with a public static int f; declared
• Other classes B, C, D, ... that extend A
• A method foo (somewhere else, doesn't matter) with the following signature: int foo(Class< A> classz);

Now I want this method implementation to return the value if the static field f, from the class represented by classz; subclasses of A may have different values. I don't want to use reflection (and neither the new jdk7 invoke.* features). For now, I have this solution that works, but isn't good, since it instanciates an object (which should not be necessary) and it generate a warning by accessing a static field from an instance:

int foo(Class< A> classz) throws [don't matter] {
    return classz.newInstance().f;
}

Any suggestions? Thanks in advance?

PS: Don't know how to type Class< ?> without the space...

解决方案

It's not really clear what you're trying to do or why you're passing in a class at all - it looks like you should just need:

int foo() {
    return A.f;
}

On success, that's what your current code will be returning anyway. Your code is equivalent to:

int foo(Class<A> classz) throws ... {
    A ignored = classz.newInstance();
    return A.f;
}

It sounds like you're trying to use polymorphism with static fields - that's simply not going to work. Static members aren't polymorphic, and neither are fields. If you're declaring extra f fields within each subclass, you would have to use reflection to get at them, but I advise you to redesign anyway. If you're not declaring extra f fields within each subclass, then you've only got one field anyway - B.f and C.f will basically resolve to A.f anyway...

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