Java: Final variables in abstract classes

Question

In Java, I can't create instances of abstract classes. So why doesn't eclipse scream about the following code?

public abstract class FooType {
    private final int myvar;

    public FooType() {
        myvar = 1;
    }
}

Answer 1

The code is fine, the final variable is initialized in the constructor of FooType.

You cannot instantiate FooType because of it being abstract. But if you create a non abstract subclass of FooType, the constructor will be called.

If you do not have an explicit call to super(...) in a constructor, the Java Compiler will add it automatically. Therefore it is ensured that a constructor of every class in the inheritance chain is called.

Answer 2

You can have constructors, methods, properties, everything in abstract classes that you can have in non-abstract classes as well. You just can't instantiate the class. So there is nothing wrong with this code.

In a deriving class you can call the constructor and set the final property:

public class Foo extends FooType
{
  public Foo()
  {
    super(); // <-- Call constructor of FooType
  }
}

if you don't specify a call to super(), it will be inserted anyway by the compiler.