None.java

public final class None<T>
    extends AbstractCollection<T>
    implements Option<T>
{

    public None() {}

    public T get() {
        throw new IllegalArgumentException("No value");
    }
    public final T getOrElse(T value) {
        return value;
    }

    public boolean isEmpty() {
        return true;
    }

    @Override
    public java.util.Iterator<T> iterator() {
        return java.util.Collections.<T>emptySet().iterator();
    }
    @Override
    public final int size() {
        return 0;
    }
}

Option.java

public interface Option<T>
    extends java.util.Collection<T>
{
    public T get();
    public T getOrElse(T deflt);
    public boolean isEmpty();
}

Some.java

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

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

    public T get() {
        return value;
    }
    public final T getOrElse(T ignored) {
        return get();
    }

    public boolean isEmpty() {
        return false;
    }

    @Override
    public final java.util.Iterator<T> iterator() {
        return java.util.Collections.<T>singleton(value).iterator();
    }
    @Override
    public final int size() {
        return 1;
    }
}