Question

I have Foo.java, which is interface.

And lots of classes that implement it. Bar1.java , Bar2.java etc.

I have a method in frontend, that is like this: getBar(String bar)

I could just do it like this:

if(bar.equals("Bar1")) {
    return new Bar1();
}

But can I somehow do it, that everytimes something new implements Foo.java , then I don’t have to update my method, with new ELSE statement.

I thought like each implementation have unique ID or something, which I add to BarX.java , whenever I create it.

Any suggestions or thoughts? I thought maybe I can use enum or smthing or any other solution.

Answer 1

FYI: You realize, of course, that you should not write this:

if(bar == "Bar1") {
    return new Bar1();
}

You should do it this way:

if("Bar1".equals(bar)) {
    return new Bar1();
}

Looks like you need a factory (aka virtual constructor). If all your Foo implementers have a default constructor, you can do this:

public class FooFactory {

    public static Foo create(Class<Foo> clazz) {
        return clazz.newInstance();
    }

    public static Foo create(String className) {
        return create(Class.forName(className));
    }
}

There are exceptions to be handled; I don’t have time to spell them out for you. You should see the idea. All you need to do is write a new class and your factory can handle it.

If there are other constructors, just elaborate the theme with parameters and additional calls. This should get you started.