Constructor Overloading in Java - Best Practice

Question

There are a few topics similar to this, but I couldn't find one with a sufficient answer.

I would like to know what is the best practice for constructor overloading in Java. I already have my own thoughts on the subject, but I'd like to hear more advice.

I'm referring to both constructor overloading in a simple class and constructor overloading while inheriting an already overloaded class (meaning the base class has overloaded constructors).

Thanks :)

Accepted Answer

While there are no "official guidelines" I follow the principle of KISS and DRY. Make the overloaded constructors as simple as possible, and the simplest way is that they only call this(...). That way you only need to check and handle the parameters once and only once.

public class Simple {

    public Simple() {
        this(null);
    }

    public Simple(Resource r) {
        this(r, null);
    }

    public Simple(Resource r1, Resource r2) {
        // Guard statements, initialize resources or throw exceptions if
        // the resources are wrong
        if (r1 == null) {
            r1 = new Resource();
        }
        if (r2 == null) {
            r2 = new Resource();
        }

        // do whatever with resources
    }

}

From a unit testing standpoint, it'll become easy to test the class since you can put in the resources into it. If the class has many resources (or collaborators as some OO-geeks call it), consider one of these two things:

Must Read

Make a parameter class

public class SimpleParams {
    Resource r1;
    Resource r2;
    // Imagine there are setters and getters here but I'm too lazy 
    // to write it out. you can make it the parameter class 
    // "immutable" if you don't have setters and only set the 
    // resources through the SimpleParams constructor
}

The constructor in Simple only either needs to split the SimpleParams parameter:

public Simple(SimpleParams params) {
    this(params.getR1(), params.getR2());
}

…or make SimpleParams an attribute:

public Simple(Resource r1, Resource r2) {
    this(new SimpleParams(r1, r2));
}

public Simple(SimpleParams params) {
    this.params = params;
}

Constructor Overloading in Java - Best Practice

5 Answers

Must Read

Make a parameter class

Sarah Jenkins