Java Optional - Why Developers Prefer Optional Values

Post Date: 12 May 2019

 

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Overview

This article discusses the use of Java Optional to introduce optional values instead of null. We will deep dive into understanding why developers prefer the Optional class to clearly communicate an optional value as opposed to a vague null representation of a variable.

This article will also illustrate the use of the functional interface in java.util.Optional to simply and reduce if-else logic in your code. In Java 8, an java.util.Optional class was introduced to treat such values at the type level to steer developers away from null-based programming. When it comes to null-safety in java, often times we are forced to write defensive code. Null checks in code has been around since the beginning. Others might argue that having a null is not the best way to represent whether a value is present or absent. Some may say that having an Optional class type will make the code a lot easier to read. Often times the source of several problems is the null reference to an object. When null is used to indicate the absence of a value, many can encounter the dangers of null.

String version = application.getFeature().getVersion();
String attrValue = application.getFeature().getAttributes().get("attr1");

The code above looks fairly reasonable. The issue occurs when the a feature is not available and a common practice is to return a null reference to represent an absence of a particular feature. The call to getVersion() will try to return a null reference, which will result in a java.lang.NullPointerException at runtime and stop your code from running.

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

public class MyApplication {
    
    public Optional<Feature> feature;

    public Optional<Feature> getFeature() {
        return feature;
    }

    public static class Feature {
        
        public String version;
        public Optional<Map<String, String>> attributes = Optional.of(new HashMap<>());

        public String getVersion() {
            return version;
        }

        public Optional<Map<String, String>> getAttributes() {
            return attributes;
        }
        
    }
    
}

The code can now be written as:

Optional<MyApplication> app = loader.loadApplication(MyApplication.class);

String version = app.flatMap(MyApplication::getFeature)
                    .map(Feature::getVersion)
                    .orElse("NO VERSION");

Optional.ofNullable(val:Object)

Creates an Optional instance of the supplied argument where the val could be absent (or not present).

String firstName = null;
System.out.println(Optional.ofNullable(firstName).isPresent());
// Output: false

Optional.of(val:Object)

Creates an Optional instance of the passed argument where the val is expected to be present (non-null value).

Example 1

Feature feature = new Feature();
Optional<Feature> optionalFeature = Optional.of(feature); 
System.out.println(Optional.of(optionalFeature).isPresent());
// Output: true

Example 2

A blank string can represent a present (non-null) value.

String firstName = "";
System.out.println(Optional.of(firstName).isPresent());
// Output: true

Replace if (var == null)

Replacing a null-based control block.

Feature feature = application.getFeature();
if (feature != null) {
    System.out.println(feature.getVersion());
}

The null check can now be replaced with:

Optional<Feature> feature = application.getFeature();
if (feature.isPresent()) {
    System.out.println(feature.get().getVersion());
}

Reduce if-else logic using functional methods

Feature feature = application.getFeature();
String version = null;
if (feature != null) {
    version = feature.getVersion();   
}
System.out.println(version);

String version = application.getFeature().map(Feature::getVersion).orElse("NO VERSION");
System.out.println(version);

Streaming calls

The following call can fail several ways when someone along the call chain a null object is returned.

String featureAttribute = app.getFeature().getAttributes().get("attr1");

An typical null-based code would look like this. You can see below how ugly the code gets and the level of nesting it generates.

String attrValue;
MyApplication app = loader.loadApplication(MyApplication.class);
if (app != null) {
    Feature feature = app.getFeature();
    if (feature != null) {
        Map<String,String> attributes = feature.getAttributes();
        if (attributes != null) {
            attrValue = attributes.get("attr1");
        }
    }   
}

The null-based code block can be replaced with the following streaming call using flatMap:

Optional<MyApplication> app = loader.loadApplication(MyApplication.class);
String attrValue = app.flatMap(MyApplication::getFeature)
                      .flatMap(MyApplication.Feature::getAttributes)
                      .map(m -> m.get("attr1"))
                      .orElse("");

The following code looks a lot cleaner and (big AND) there’s no literal null checks.

Conclusion

The Optional-based programming would be best for you to protect your code against null pointers exceptions. The goal of java.lang.Optional will not replace all null reference in your code but rather help create a better and cleaner code.

 

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