Peter: others have mentioned it, but I'll chime in.  This is exactly 
what ERC.java does.  Check it out!

Your approach below will not work for you.  Rather, it will create a 
node which returns a different value every time it is called.  Sort of 
like the GP node equivalent of        (random 10.0)

Sean

Peter Thieu wrote:
> Hi there
> 
> i want leaves with a constant, i.e:
> 
> public class Const extends GPNode
>   {
>     private int cValue;
>   public String toString() { return Integer.toString(this.cValue);}
> 
>   public void checkConstraints(final EvolutionState state,
>                                final int tree,
>                                final GPIndividual typicalIndividual,
>                                final Parameter individualBase)
>       {
>       super.checkConstraints(state,tree,typicalIndividual,individualBase);
>       if (children.length!=0)
>           state.output.error("Incorrect number of children for node " +
>                              toStringForError() + " at " +
>                              individualBase);
>       }
> 
>   public void eval(final EvolutionState state,
>                    final int thread,
>                    final GPData input,
>                    final ADFStack stack,
>                    final GPIndividual individual,
>                    final Problem problem)
>       {
>       DoubleData rd = ((DoubleData)(input));
>       this.cValue = ((int)(state.random[thread].nextDouble()*10));
>       rd.x = this.cValue;
>       }
>   }
> 
> assuming it creates a tree like (x+2) * 3, where 2 and 3 leaves were 
> produced by the class Const
> 
> assuming this tree is passed to the next generation, will it be the same 
> tree with the same constants (x+2) * 3, or will there be new constants 
> values i.e. (x+4) * 5?
> 
> kind regards
> 
> Peter