Question

I have the following class:

public abstract class A
{
  public abstract String doSomething(String X, String Y);
  public static String doSomething(String X, String Y){return X + Y;}
  ...
}

The issue I have is that the static and abstract doSomething() methods seem to clash as duplicates. I thought this should be fine because the static method belongs to the class, not an instance of the class, so I was going to use the abstract method to enforce the method on all subclasses and the static method as a helper so that I have nicely factored code.

I know I could probably add an interface into the mix, but I don’t really understand what’s wrong with my abstract and static methods existing on the same class. What’s wrong with this?

Answer 1

In Java it is valid (despite being misleading and confusing) to call a static method from an object instance rather than the class name (despite warnings generated by many compilers).

System.out.println(String.valueOf(true)); // Prints "true".
System.out.println("".valueOf(true)); // Prints "true", unfortunately.

So the following seemingly valid code wouldn’t know which of those methods to call:

A a = getInstanceOfConcreteSubclassOfA();
a.doSomething(null, null); // Compiler can't decide which method to call...

Unfortunately, it’s just one of the few ugly corners of the Java language.