Java - Abstract class to contain variables?

Question

Is it good practice to let abstract classes define instance variables?

public abstract class ExternalScript extends Script {

    String source;

    public abstract void setSource(String file);

    public abstract String getSource();
}

The sub class, ExternalJavaScript.class, would then automatically get the source variable but I feel it's easier to read the code if all the sub classes themselves define the source, instead of from inheritance.

What is your advice?

/Adam

Answer 1

I would have thought that something like this would be much better, since you're adding a variable, so why not restrict access and make it cleaner? Your getter/setters should do what they say on the tin.

public abstract class ExternalScript extends Script {

    private String source;

    public void setSource(String file) {
        source = file;
    }

    public String getSource() {
        return source;
    }
}

Bringing this back to the question, do you ever bother looking at where the getter/setter code is when reading it? If they all do getting and setting then you don't need to worry about what the function 'does' when reading the code. There are a few other reasons to think about too:

• If source was protected (so accessible by subclasses) then code gets messy: who's changing the variables? When it's an object it then becomes hard when you need to refactor, whereas a method tends to make this step easier.
• If your getter/setter methods aren't getting and setting, then describe them as something else.

Always think whether your class is really a different thing or not, and that should help decide whether you need anything more.