problem with builders

Eva Krejcirova eva.krejcirova at
Tue Jul 17 02:29:33 PDT 2012

Hi Jose,

There is another solution for your problem - if you write your code like 
this, it should compile:
LabelBuilder<?> lb = LabelBuilder.create();
Label label = lb.text("txt").build();


On 7/17/2012 8:44 AM, John Hendrikx wrote:
> This is because the Builder classes are actually generic to make it 
> possible to subclass them, but still make it possible to return the 
> correct type.  For example, a RectangleBuilder builds Rectangles, but 
> it extends ShapeBuilder which builds Shapes.  In order for the 
> extended ShapeBuilder to know it should return RectangleBuilder for 
> the intermediate steps there is a generic parameter passed by 
> RectangleBuilder:
> public class RectangleBuilder<B extends RectangleBuilder<B>> extends 
> ShapeBuilder<B>
> B here is RectangleBuilder.
> Now, because you are using raw types in your code (you did not specify 
> the generic type for RectangleBuilder for example) and are calling 
> methods that are not part of RectangleBuilder directly (fill is from 
> ShapeBuilder) it cannot determine the correct type anymore when build 
> is called.  You can resolve it by writing the code like this:
>           Label label = LabelBuilder.create().text("txt").build();
>           StackPane sp = 
> StackPaneBuilder.create().alignment(Pos.CENTER).build();
>           Rectangle r = 
> RectangleBuilder.create().fill(Color.ALICEBLUE).build();
> On a side note, I've written such Builder constructs before, and there 
> is another way Oracle could have handled this -- they could have made 
> the final Builder implementations non-generic and then you could write 
> the code as you did -- it would however introduce another class for 
> each builder...
> public abstract class AbstractRectangleBuilder<B> extends 
> AbstractShapeBuilder<B>
> public final class RectangleBuilder extends 
> AbstractRectangleBuilder<RectangleBuilder>
> Now the final class, which is used by users, is not generic and can be 
> used like you are doing without any problems at all.
> --John
> On 17/07/2012 03:55, Jose Martinez wrote:
>> I am having a problem with some of the builders.... maybe I'm doing 
>> something wrong.  If I instantiate a builder (e.g. LabelBuilder) then 
>> if I edit it (e.g. .text("txt") ) then the compiler complaints that 
>> the build() method is not present.  Its as if the .text() method does 
>> not returns a LabelBuilder.  It does not happen with all builders, I 
>> have not tested enough to pick up on a pattern.
>> Here are some examples.....
>> //will not compile
>>          LabelBuilder lb = LabelBuilder.create();
>>          Label label = lb.text("txt").build();
>>          //compiles
>>          StackPaneBuilder spb = StackPaneBuilder.create();
>>          StackPane sp = spb.alignment(Pos.CENTER).build();
>>          //will not compile
>>          RectangleBuilder rb = RectangleBuilder.create();
>>          Rectangle r = rb.fill(Color.ALICEBLUE).build();
>> thanks jose

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