Java Option Class

Implementation of Scala Option in Java.

Usage

Including in Maven

Available from the Guardian github repository:

<dependency>
    <groupId>com.gu</groupId>
    <artifactId>option</artifactId>
    <version>1.2</version>
</dependency>

And check for the latest version number.

Creating options

import static com.gu.option.Option.none;
import static com.gu.option.Option.some;
import static com.gu.option.Option.option;
import com.gu.option.Option;

...

Option<Integer> s1 = some(6174);
Option<Integer> n1 = none();
Option<Integer> s2 = option(6174);   // is Some(6174)
Option<Integer> n2 = option(null);   // is None

You may have a headache with ensuring correct typing if you use none() in expressions.

Accessing options

Iterable for-syntax is available:

Option<Integer> s = some(6174);
Option<Integer> n = none();

for (Integer i : s) {
// Do something with i = 6174
}

for (Integer i : n) {
    // Not executed
}

As are get and getOrElse: Option s = some(6174); Option n = none();

System.out.println(s.get());            // prints 6174
System.out.println(s.getOrElse(5740));  // prints 6174
System.out.println(n.getOrElse(5740));  // prints 5740

Operating with functions and Options

To map, flatMap, foreach, etc on Options, function interfaces are provided:

import com.gu.option.Option.Function;
import com.gu.option.Option.UnitFunction;

Option<Integer> s = some(1);
Option<Integer> n = none();

final Function<Integer,Integer> f = new Function<Integer,Integer>() {
   public Integer apply(Integer x) { return x * 2; }
};

System.out.println(s.map(f));        // prints Some(2)
System.out.println(n.map(f));        // prints None

final Function<Integer,Option<Integer>> f2 = new Function<Integer,Option<Integer>>() {
   public Option<Integer> apply(Integer x) { return some(x * 2); }
};

System.out.println(s.flatMap(f2));   // prints Some(2)
System.out.println(n.flatMap(f2));   // prints None

final UnitFunction<Integer> f3 = new UnitFunction<Integer>() {
   public void apply(Integer x) { System.out.println(x * 2); }
};

s.foreach(f3);                      // prints 2
n.foreach(f3);                      // does nothing

Filtering and testing

The methods isDefined, isEmpty, filter, exists are implemented as their Scala counterparts.