如何在Java中实现抽象的单例类？ [英] How can I implement an abstract singleton class in Java?

问题描述

以下是我的示例抽象单例类：

Here is my sample abstract singleton class:

public abstract class A {
    protected static A instance;
    public static A getInstance() {
        return instance;
    }
    //...rest of my abstract methods...
}

以下是具体实现：

public class B extends A {
    private B() { }
    static {
        instance = new B();
    }
    //...implementations of my abstract methods...
}

不幸的是我无法在B类中获取静态代码来执行，因此实例变量永远不会被设置。我试过这个：

Unfortunately I can't get the static code in class B to execute, so the instance variable never gets set. I have tried this:

Class c = B.class;
A.getInstance() - returns null;

此

ClassLoader.getSystemClassLoader().loadClass("B");
A.getInstance() - return null;

在eclipse调试器中运行这两个，静态代码永远不会被执行。我可以找到执行静态代码的唯一方法是将B的构造函数的可访问性更改为public，并调用它。

Running both these in the eclipse debugger the static code never gets executed. The only way I could find to get the static code executed is to change the accessibility on B's constructor to public, and to call it.

我正在使用sun-java6 -jre在Ubuntu 32bit上运行这些测试。

I'm using sun-java6-jre on Ubuntu 32bit to run these tests.

推荐答案

抽象Singleton？对我来说听起来不太可行。 Singleton模式需要一个 private 构造函数，这已经使得子类化成为不可能。你需要重新考虑你的设计。 抽象工厂模式可能更适合特定用途。

Abstract Singleton? Doesn't sound viable to me. The Singleton pattern requires a private constructor and this already makes subclassing impossible. You'll need to rethink your design. The Abstract Factory pattern may be more suitable for the particular purpose.

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