package basics.mutablebasic;
import basics.immutabledata.Pair;
public class Main {
  private Main() {}
  static public void main (final String[] args) {
    //stdlib.Trace.graphvizShowSteps (true); stdlib.Trace.run ();
    final PairBuilder<Integer,String> pb1 = new PairBuilder<Integer,String>();
    pb1.setFirst(42);
    pb1.setSecond("dog");
    System.out.println(pb1);
    final Pair<Integer,String> p1 = pb1.toPair();
    System.out.println(p1);

    final PairBuilder<Integer,String> pb2 = new PairBuilder<Integer,String>();
    final Pair<Integer,String> p2 = pb2.toPair();
  }
}
final class PairBuilder<S extends Comparable<S>, T extends Comparable<T>> {
  private S x;
  private T y;
  public PairBuilder() { }
  public void setFirst(S x) { this.x = x; }
  public void setSecond(T y) { this.y = y; }
  public Pair<S,T> toPair() {
    if (x == null || y == null)
      throw new NullPointerException();
    return new Pair<S,T>(x,y);
  }
}