Option pattern from FP for Java Developers

gistfile1.java

public final class Some<T> extends Option<T> { 
  private final T value;

  public Some(T value) { 
    this.value = value; 
  } 

  public boolean hasValue() { 
    return true; 
  } 

  public T get() { return value; }

  @Override
  public String toString() { return "Some("+value+")"; }

  @Override
  public boolean equals(Object other) {
    if (other == null || other.getClass() != Some.class) 
      return false;
    Some<?> that = (Some<?>) other; Object thatValue = that.get(); return value.equals(thatValue);
  }

  @Override
  public int hashCode() { 
    return 37 * value.hashCode(); 
  } 
}


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; } 
}