Java - Alternatives to forcing subclass to have a static method

Question

I often find I want to do something like this:

class Foo{
public static abstract String getParam();
}

To force a subclasses of Foo to retur

Answer 1

I'm having the same problem over and over again and it's hard for me to understand why Java 8 preferred to implement lambda instead of that.

Anyway, if your subclasses only implement retrieving a few parameters and doing rather simple tasks, you can use enumerations as they are very powerful in Java: you can basically consider it a fixed set of instances of an interface. They can have members, methods, etc. They just can't be instanciated (as they are "pre-instanciated").

public enum Processor {
    PROC_IMAGE {
        @Override
        public String getParam() {
            return "image";
        }
    },

    PROC_TEXT {
        @Override
        public String getParam() {
            return "text";
        }
    }
    ;

    public abstract String getParam();

    public boolean doProcessing() {
        System.out.println(getParam());
    }
}

The nice thing is that you can get all "instances" by calling Processor.values():

for (Processor p : Processorvalues()) {
    System.out.println(String.format("Param %s: %s", p.name(), p.getParam()));
    p.doProcessing();
}

If the processing is more complex, you can do it in other classes that are instanciated in the enum methods:

@Override
public String getParam() {
    return new LookForParam("text").getParam();
}

You can then enrich the enumeration with any new processor you can think of.

The down side is that you can't use it if other people want to create new processors, as it means modifying the source file.