David Graham wrote:
Static methods are evil for many reasons including philosophical (they're not OO) and practical (you can't override their behavior). You should use a Singleton class with non-static methods.
And the generally accepted way to get a reference to the singleton is with a static "getInstance" method, right? Is there any way to make an anonymous subclass of a Singleton that uses a static method to get the instance? For example:
public class SubclassSingleton {
public static void main(String[] args) {
MySingleton ms = new MySingleton() {
int doSomething() {
return 42;
}
} MySingleton inst = ms.getInstance();
System.out.println(ms.doSomething());
}
}class MySingleton {
static MySingleton me;
static getInstance() {
if (MySingleton.me == null)
MySingleton.me = new MySingleton();return MySingleton.me; }
int doSomething() {
return 8;
}
}This simple code doesn't work, because even if you subclass the singleton and override one of the methods, the getInstance() method will create a base-class MySingleton. And since this method is static, it can't be overridden. So while singletons are useful, you can't use them in anonymous subclasses (as far as I can tell), which makes them difficult to use with mock object unit testing.
Please someone point out the flaw in my reasoning, it has bothered me for quite a while and I'd love to be proven wrong.
Erik
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