Question

I have created factory class and i wonder which is better way to implement it.
option 1

public class Factory {

    private IProperty prop;
    public IDoc doc;

    public Factory(int version) {
        switch (version) {
            case '1':   
                prop = new Prop();
                doc = new Docu();
        ...
            case '2':
            prop = new Prop1();
            doc = new Docu1();
        ...
        }
    }

    public IProperty getProperty() {
        return this.prop;
    }

    public IDoc getDoc() {
        return this.doc;
    }
}

My question is if to do it like that i.e. define member with the interface type and to to switch on the constructor or for every get method to use switch statement instead on the constructor, so in the constructor i will just get the
version and save it on class member and than for instance use like

public IProperty getProperty() {
switch (version) {
  case '1':
    prop = new Prop();
  case '2':
    prop = new Prop1();
...

So what is the better way, or any other idea?

Answer 1

• First of all, your Factory should ideally have static references
  instead of non-static one. And it should have a static method to create / get
  the appropriate instance.

• Secondly, its better to have two different factories for different
  types.

• Thirdly, I would name your method as createProperty, rather than
  getPropertyObject, because that method is not returning the already
  created instance, rather its creating one.

Of course, getPropertyObject('1'), seems like it is fetching a property for that version from a persistence storage, which is not what it is doing. It is rather creating an instance based on version.

(NOTE: – Name of static factory methods are important. They are amongst one of the advantages, they have over constructors. Since with a name, you can guess what exactly that factory method does)

Having said that, I would say, that the 2nd option would be better with all those changes. Let the createProperty method decide, how it wants to create the instance.

So, I would modify your code like this: –

public class PropertyFactory {
    private static IProperty prop;

    public static createProperty(char version) {

        switch (version) {
            case '1':
                prop = new Prop();
                break;  // Don't forget a `break` here.
            case '2':
               prop = new Prop1();
               break;

            default:  // do have a default case
               prop = null;
        } 
        return prop;
    }
}

Similarly, you can create a DocumentFactory to create a document object. Name the method: – createDocument(char version)