How to improve the builder pattern?

Question

Motivation

Recently I searched for a way to initialize a complex object without passing a lot of parameter to the constructor. I tried it with the builder pattern,

Answer 1

Why don't you put "needed" parameters in the builders constructor?

public class Complex
{
....
  public static class ComplexBuilder
  {
     // Required parameters
     private final int required;

     // Optional parameters
     private int optional = 0;

     public ComplexBuilder( int required )
     {
        this.required = required;
     } 

     public Builder setOptional(int optional)
     {
        this.optional = optional;
     }
  }
...
}

This pattern is outlined in Effective Java.