Reusing code in overloaded constructors

Question

My BigBlock class needs a few overloaded constructors. All of them need to initialize the same few fields in the same way.

What is the proper way to do this? Is it to make a function, e.g. Initialize in the example below, that does these things, and have all constructors call that function?

public class BigBlock {
    private Thing parentThing;
    Units lengthUnit;
    LabCoordinateSystem labCoordinateSystem;

    private void Initialize(){
        lengthUnit = parentThing.getPreferredUnits(0);
        labCoordinateSystem = parentThing.getCoordinateSystem();
    }

    BigBlock(Thing myThing){
        parentThing= myThing;
        Initialize();
    }

    BigBlock(Thing myThing, double x, double y, double z){
        parentThing= myThing;
        Initialize();
        // more code involving x, y, z
    }

    // a few more constructors

}

Answer 1

Typically it's best to make all constructors chain to a single one which contains the most information, e.g.

BigBlock(Thing myThing) {
    this(myThing, 0, 0, 0); // Assuming 0 is the default value for x, y and z
}

It becomes slightly weirder if there are different ways to call the constructor which don't effectively represent subsets of the same information - but at that point I'd say there's a design smell anyway.

Note that by the time you've got all the real logic in a single constructor, you don't need your Initialize method (which should be initialize to follow Java naming conventions, btw) at all - which may also you can make fields final which previously you couldn't have done.

Answer 2

Just reuse your current constructor. Let every other constructor call the one that initialises all required values.

BigBlock(Thing myThing){
    parentThing = myThing;
    lengthUnit = parentThing.getPreferredUnits(0);
    labCoordinateSystem = parentThing.getCoordinateSystem();

}

BigBlock(Thing myThing, double x, double y, double z){
    this(myThing);
    // more code involving x, y, z
}

If x,y and z need to be part of the initalization, BigBlock(Thing myThing) should call BigBlock(Thing myThing, double x, double y, double z) with default values.