从抽象类继承静态变量 [英] Inheriting static variable from abstract class

问题描述

我有六个类，它们都扩展了相同的抽象类。抽象类有一个静态变量，指向一些JNI代码，我只想在每个类的实例化时加载一次。

I have half a dozen classes which all extend the same abstract class. The abstract class has a static variable pointing to some JNI code that I only want to load once per instantiation of the classes.

据我所知，这导致这个静态变量的一个实例被实例化，但我想要的是每个扩展类都有自己的静态实例给定子类唯一的变量。我想在我的抽象类中编写一些代码来修改和/或释放抽象类。是否有可能同时完成这两件事？

From what I understand this results in exactly one instance of this static variable being instantiated, but what I want is for each of the extending classes to have their own static instance of the variable that is unique for the given child class. I want to write some code in my abstract class that modifies and/or releases the abstract class. Is it possible to do both of these things at once?

因此，我可以编写一个带有变量foo的抽象类栏和一个打印内容的printFoo方法foo。然后我按顺序实例化fooBar1，fooBar2和fooBar3，每个扩展bar类并将foo初始化为静态块中的不同值。如果我调用 foobar1.printFoo 我想打印由fooBar1构造函数初始化的foo的静态值。

So as an example can I write an abstract class bar with an variable foo and a printFoo method which prints the content of foo. Then I instantiate in order fooBar1, fooBar2, and fooBar3 which each extend the bar class and initialize foo to different values in static blocks. If I call foobar1.printFoo I want to print the static value of foo initialized by fooBar1 constructor.

这可以可以在java中完成吗？

Can this be done in java?

推荐答案

你可以近似它，但是每个子类需要单独的静态变量，以阻止子类覆盖彼此的价值观。最简单的方法是通过getter getFoo 对它进行抽象，以便每个子类从正确的位置获取foo。

You can approximate it, but you will need separate static variables for each subclass, to stop subclasses overwriting each others values. It's easiest to abstract this via a getter getFoo so that each subclass fetches the foo from the right place.

Something像这样

Something like this

abstract class Bar
{
   // you don't have to have this in the base class 
   // - you could leave out the variable and make
   // getFoo() abstract.
   static private String foo;

   String getFoo() {
     return foo;
   }

   public void printFoo() {
      System.out.print(getFoo());
   }
}

class Foo1 extends Bar
{
   static final String foo1;

   public String getFoo() {
      return foo1;  // return our foo1 value
   }

   public Foo1() {
      foo1 = "myfoo1";
   }
}


class Foo2 extends Foo1
{
   static final String foo2;

   public String getFoo() {
      return foo2;  // return our foo2 value
   }

   public Foo2() {
      foo2 = "myfoo2";
   }
}

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