Builders/Factories and Inheritance.

Daniel Pitts <>
Sat, 16 Aug 2008 10:58:20 -0700
I was just thinking about the Builder pattern (because of Roedy's recent

It seems to me that Builders are a special type of Factory, and in
general Factories /tend/ to prevent the client from specifying the
actual implementation to use. I was thinking about ways to give the
client some control, while allowing the builder to do its job as-well.

I was thinking of a double-indirection factory (bad name maybe?)

class Foo { public Foo(int bar, Baz baz) {} }

interface FooFactory {
   Foo createFoo(int bar, Baz baz);

class FooBuilder {
   private final FooFactory factory;
   public FooBuilder(FooFactory factory) {this.factory = factory;}
   public FooBuilder() {this.factory = new DefaultFooFactory();}
   // builder methods etc...

   public Foo toFoo() { return factory.createFoo(getBar(), getBaz()); }

This gives the client the ability to create a subclass foo builder, and
utilize the foo builder:
class SpecialFoo extends Foo {
    SpecialFoo(int bar, Baz baz, Zip zip) {
       super(bar, baz);

class SpecialFooBuilder implements FooFactory {
    // builder methods to get "zip"
    Foo createFoo(int bar, Baz baz) {
     return new SpecialFoo(bar, baz, zip);

class Client {
   public void stuff() {
       SpecialFooBuilder specialFooBuilder = new SpecialFooBuilder();
       FooBuilder fooBuilder = new FooBuilder(specialFooBuilder);

This seems like it *might* be an anti-pattern, but I'm not sure. Have
any of you had to implement this design? How did it work out? I don't
actually have any real code for this, since I'm just thinking "out loud"
at the moment.
Daniel Pitts' Tech Blog: <>

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