None.java

public final class None<T> extends Option<T> {
  public static class NoneHasNoValue extends RuntimeException {}

  public None() {}

  public boolean hasValue() { return false; }

  public T get() { throw new NoneHasNoValue(); }

  @Override
  public String toString() { return "None"; }

  @Override
  public boolean equals(Object other) {
    return (other == null || other.getClass() != None.class) ? false : true;
  }

  @Override
  public int hashCode() { return -1; }
}