Cleaner way of creating multiple objects from base class

Question

Let's say I have a class, called BaseClass, that looks something like this

class BaseClass{
    String var1;
    int var2;

    public void methodToBeOverridden(){}
}

and I need to create a significant number of classes that inherit this class. They will all override methodToBeOverridden(), but will all be instantiated in a static context. Since they all need to be static, they cannot be put in a single .class file to my understanding. Is there any cleaner way to do this than creating a separate .class file for each instance? I really doubt there is, but I thought I'd ask here before I got started on it just in case.

You can create static nested classes in the same class file. You can also declare more than one top-level class in a file if they're not public, but that's generally discouraged. — shmosel
– shmosel, Commented Aug 16, 2016 at 0:22
I don't think this BaseClass is necessary. I suggest use enum to implement it. — MageXellos
– MageXellos, Commented Aug 16, 2016 at 0:31
Maybe also a job for a functional interface and method handles. You can have all variants in a single class. — eckes
– eckes, Commented Aug 16, 2016 at 0:56

Peter Lawrey · Accepted Answer · 2016-08-16 00:32:14Z

An approach I take is to override implementations for an enum which implements an interface From https://github.com/OpenHFT/Chronicle-Engine/blob/master/src/main/java/net/openhft/chronicle/engine/map/remote/MapFunction.java

public enum MapFunction implements SerializableBiFunction<MapView, Object, Object> {
    CONTAINS_VALUE {
        @Override
        public Boolean apply(@NotNull MapView map, Object value) {
            Class vClass = map.valueType();
            return map.containsValue(convertTo(vClass, value));
        }
    },
    REMOVE {
        @Override
        public Object apply(@NotNull MapView map, Object o) {
            Class kClass = map.keyType();
            Class vClass = map.valueType();
            KeyValuePair kf = (KeyValuePair) o;
            return map.remove(convertTo(kClass, kf.key), convertTo(vClass, kf.value));
        }
    },
    REPLACE {
        @Override
        public Object apply(@NotNull MapView map, Object o) {
            Class kClass = map.keyType();
            Class vClass = map.valueType();
            if (o instanceof KeyValuePair) {
                KeyValuePair kf = (KeyValuePair) o;
                return map.replace(convertTo(kClass, kf.key), convertTo(vClass, kf.value));
            }
            KeyValuesTuple kf = (KeyValuesTuple) o;
            return map.replace(convertTo(kClass, kf.key), convertTo(vClass, kf.oldValue), convertTo(vClass, kf.value));
        }
    },

This allows me to have many implementations of the same method in a single .java file. Note: this still creates multiple .class files.

I'm not gonna lie, I have no idea what a lot of that was. But you steered me in the direction of enums, which worked flawlessly.

djechlin · Accepted Answer · 2016-08-16 00:27:18Z

0

I seriously doubt that each of these classes has substantially different code inside methodToBeOverridden. They probably all differ by some piece of data - or maybe they fall into a few families like that - and you should make that piece of data be a constructor argument to the class and not have very few derived classes if any.

answered Aug 16, 2016 at 0:27

djechlin

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3 Comments

user207421 Over a year ago

You seriously doubt based on what evidence? Or is this mere guesswork?

djechlin Over a year ago

@EJP based on my experience in Java. Just sounds like a design smell and this is probably why. I'd be interested if the OP posts more but in the meantime I've likely left a pretty substantial hint that hopefully will get them to stop coding into a hole. I also may be wrong, which is fine.

senox13 Over a year ago

You know what they say about making assumptions. ;)

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