Inheritance and static factory methods

Question

I have programmed a java.util.logging.Formatter (named OneLineFormatter) for my console outputs. It has two static factory methods, both call the private constructor.

Now I wanted to program a second one for debugging purposes (named DebugFormatter), which only overrides the method formatRecord in OneLineFormatter so the traces are printed too instead of just the localized message and the class.

Eclipse warned me that the super constructor OneLineFormatter() is undefined and I have to invoke another constructor. I googled the problem and found this: Java error: Implicit super constructor is undefined for default constructor on StackOverflow. But I do not want to create a public constructor because that would be against the factory principle. The factory methods and the constructor can be the same (the DebugFormatter factory methods should create a new DebugFormatter instead of a OneLineFormatter though).

If you need some more info just ask. Thanks for your help in advance!

The code:

public class OneLineFormatter extends Formatter {
    public static Formatter withPackageFromRoot(String rootName) {
        return new OneLineFormatter(rootName);
    }

    public static Formatter withClassOutputOnly() {
        return new OneLineFormatter("");
    }

    private String rootName;

    private OneLineFormatter(String rootName) {
        this.rootName = rootName;
    }

    @Override
    public String format(LogRecord record){<code>}

    private String formatRecord(LogRecord record{<code that I want to override>}
}

And the second class:

public class DebugFormatter extends OneLineFormatter {
    public static Formatter withClassOutputOnly() {
        return new DebugFormatter("");
    }

    public static Formatter withPackageFromRoot(String rootName) {
        return new DebugFormatter(rootName);
    }

    private DebugFormatter(String rootName) {<same as OneLineFormatter(String)>}

    @Override
    private String formatRecord(LogRecord record) {<code>} 

}

EDIT 1: added code EDIT 2: corrected code

please include your code inside the question. Without it it´s a lot harder to analyze where something is done wrong by just reading your description. — SomeJavaGuy, Mar 29 '16 at 13:01
I would splice your OneLineFormater code from the factory. So you can extend the OnlineFormater instead of the factory. — Rene M., Mar 29 '16 at 13:04
@ReneM. The factory methods can stay the same, I just want to override the method formatRecord(LogRecord) in OneLineFormatter — kaesaecracker, Mar 29 '16 at 13:11
You could also just make the constructor `package-private`, or `protected`. This way you´d be able to acces the constructor in either the same package, or additionally in every subclass. — SomeJavaGuy, Mar 29 '16 at 13:17
@KevinEsche Oh, thats exactly what I wanted, thanks! If you share it as an answer I will mark this Question as answered. — kaesaecracker, Mar 29 '16 at 13:21

score 1 · Accepted Answer · answered Mar 29 '16 at 13:23

You could just make the constructor for OneLineFormatter package-private or protected. This way you could reduce the access to the constructor to a point that fits your needs

OneLineFormatter(String rootName) {
    this.rootName = rootName;
}
// OR 
protected OneLineFormatter(String rootName) {
    this.rootName = rootName;
}

Inheritance and static factory methods

1 Answers1