Another scala option in java

Scala on valentine’s day is still awesome! I was doing some standard java development today and it remembered me a guy who use a custom implementation of scala option in java because he really missed it (I must admitted, I was in the same mood). I google it and found some interesting simple implementation. Here’s what I did on my side based on The “Option” Pattern.

package com.synhaptein;

public abstract class Option<T> implements Iterable<T> {
  public static None None = new None<Object>();
  public static <T> Some<T> Some(T p_value) {
    return new Some<T>(p_value);
  }

  public abstract T get();
  public abstract T getOrElse(T p_value);
}

package com.synhaptein;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Some<T> extends Option<T>  {
  private T m_value;

  public Some(T p_value) {
    m_value = p_value;
  }

  public Iterator<T> iterator() {
    List<T>  list = new ArrayList<T>();
    list.add(m_value);
    return list.iterator();
  }

  @Override
  public T get() {
    return m_value;
  }

  @Override
  public T getOrElse(T p_value) {
    return m_value;
  }
}

package com.synhaptein;

import java.util.Collections;
import java.util.Iterator;

public class None<T> extends Option<T> {
  public Iterator<T> iterator() {
    return Collections.<T>emptyList().iterator();
  }

  public T get() {
    throw new UnsupportedOperationException("Cannot resolve value on None");
  }

  public T getOrElse(T p_value) {
    return p_value;
  }
}

Here’s my personal addition: import static! It removes the need of adding new Some or new None so it feels more like scala. The downside is that None is not typed with T… but it's not null!

package com.synhaptein;
import static com.synhaptein.Option.*;

public class OptionTests {

  public static void printOption(Option<String> p) {
    System.out.println(p.getOrElse("Doe"));
  }

  public static void main(String[] args) {
    Option<String> firstName = Some("test");
    Option<String> lastName = None;

    printOption(None);
    printOption(firstName);

    try {
      System.out.println(lastName.get());
    }
    catch (UnsupportedOperationException e) {
      System.out.println("Should throw an exception");
    }

    for(String s : firstName) {
      System.out.println(s);
    }
  }
}

Another scala option in java

Written by

Philippe L'Heureux

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