Question

Is it possible to define a private abstract class in Java? How would a Java developer write a construct like below?

public abstract class MyCommand {
    public void execute()
    {
        if (areRequirementsFulfilled())
        {
            executeInternal();
        }
    }
    private abstract void executeInternal();
    private abstract boolean areRequirementsFulfilled();
}

Answer 1

You can’t have private abstract methods in Java.

When a method is private, the sub classes can’t access it, hence they can’t override it.

If you want a similar behavior you’ll need protected abstract method.

It is a compile-time error if a method declaration that contains the keyword abstract also contains any one of the keywords private, static, final, native, strictfp, or synchronized.

And

It would be impossible for a subclass to implement a private abstract method, because private methods are not inherited by subclasses; therefore such a method could never be used.

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Resources :

• JLS – 8.4.3. Method Modifiers
• JLS – 8.4.3.1. abstract Methods