Options

Functional Option that can be used with Java 1.6 and Android.

Option

Similar to Java 8 Optional but targeting Android and Java 6.

Why to use them?

In 1965, Sir Tony Hoare introduced null reference. Since then he apologised for that and called it The Billion Dollar Mistake. If the inventor of null pointers and references has condemned them, why the rest of us should be using them?

Where to use them?

Currently there are several ways to say that an object could be null. Most popular way in Android nowadays is using Nullable or NonNull annotations. The problem with those annotations is that you cannot say what kind of objects are in an array, or if you use Rx, in an Observable. With Options you can use instead List<Option<String>> or in Rx Observable<Option<Integer>>.

How to use them?

If you have been using RxJava, this API will look really similar to RxJava. Still Option is synchronous API that does not have too much to do with Reactive Programming.

Basic usage

Code with nulls:

String input = ...;
String result = null;

if (input != null && input.length() > 0) {
    result = "Length of the string is " + input.length();
} else {
    result = "The string is null or empty";
}

Code with Options:

String input = ...;

String result = Option.ofObj(input)
                      .filter(str -> str.length() > 0)
                      .match(str -> "Length of the string is " + str.length(),
                             ()  -> "The string is null or empty");

Advance usage

Code with nulls:

String input = ...;
String result = null;

if (input != null) {
    try {
        int intValue = Integer.parseInt(input);
        result = "Input can be parsed to number: " + intValue;
    } catch (NumberFormatException e) {
        result = "Input is not a number";
    }
}

Code with Options:

String input = ...;

String result = Option.ofObj(input)
                      .flatMap(str -> Option.tryAsOption(() -> Integer.parseInt(str)))
                      .map(intValue -> "Input can be parsed to number: " + intValue)
                      .orDefault(() -> "Input is not a number");

How to include in your project?

Options are available on maven via jitpack. Just add to your gradle files:

To your top level gradle.build file add repository:

repositories { 
    jcenter()
    maven { url "https://jitpack.io" }
}

To your module level gradle.build add dependency:

dependencies {
    // other dependencies
    implementation 'com.github.tomaszpolanski:options:1.3.0'
}

Can I use it with Kotlin?

Sure, you can, but I would recommend using Peter Tackage's kotlin-options as they play nicer with Kotlin.

References

This library was strongly influenced by C# Functional Language Extensions.