java version of scala Option

Option.java

package fupfin;

import java.util.NoSuchElementException;

/**
 * A base class of simple value container that represents optional values. You can 
 * use subclass Some<A> for some existent values or None for non existent values.
 * This is java version of scala Option class. 
 *
 * @author fupfin@gmail.com
 * @see scala.Option
 * @param <T> type of the contained value
 */
public abstract class Option<T> {

    public abstract T get();
    public abstract T getOrElse(T defaultValue);
    public abstract boolean isDefined();
    public abstract boolean isEmpty();
    
    public static final Option<Object> NONE = new None();
    
    @SuppressWarnings("unchecked")
    public static <A> Option<A> none() {
        return (Option<A>) NONE;
    }
    
    public static <A> Option<A> some(A value) {
        return new Some<A>(value);
    }
    
    public static class Some<T> extends Option<T> {

        private T value;
        
        public Some(T value) {
            super();
            this.value = value;
        }
        
        @Override 
        public final T get() {
            return value;
        }
        
        @Override
        public final T getOrElse(T defaultValue) {
            return get();
        }

        @Override 
        public final boolean isDefined() { return true; }
        
        @Override 
        public final boolean isEmpty() { return !isDefined(); }
    }
    
    public static class None extends Option<Object> {
        
        private None() {
            super();
        }

        @Override public Object get() {
            throw new NoSuchElementException();
        }
        
        @Override public Object getOrElse(Object defaultValue) {
            return defaultValue;
        }
        
        @Override public boolean isDefined() { return false; }
        @Override public boolean isEmpty() { return true; }
    };
}

OptionTest.java

package fupfin;

import static fupfin.Option.*;
import static org.junit.Assert.*;

import java.util.NoSuchElementException;

import org.junit.Test;

public class OptionTest {

    private static final String TEST_STRING = "a";

    @Test
    public void testNone() {
        Option<String> result = none();
        assertFalse(result.isDefined());
        assertTrue(result.isEmpty());
        assertSame(result, NONE);
        assertTrue(Option.None.class.isInstance(result));
    }
    
    @Test
    public void testGetOrElseForNone() {
        Option<String> result = none();
        assertSame(TEST_STRING, result.getOrElse(TEST_STRING));
    }

    @Test(expected=NoSuchElementException.class)
    public void testGetDataFromNone() {
        Option<String> result = none();
        result.get();
        fail();
    }

    @Test
    public void testSome() {
        Option<String> result = some(TEST_STRING);
        
        assertTrue(result.isDefined());
        assertFalse(result.isEmpty());
        assertEquals(TEST_STRING, result.get());
        assertTrue(Option.Some.class.isInstance(result));
    }
    
    @Test
    public void testGetOrElseForSome() {
        Option<String> result = some(TEST_STRING);
        assertSame(TEST_STRING, result.getOrElse(null));
    }
 }