The article was initially published at carloschac.in

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🎩 Immutability in Java 🔥 Made Easy

Carlos Chacin ☕👽 ・ Apr 12 ・ 10 min read

#java #bestpractices #immutability

In this article, we are going to compare some of the features of the Immutables.org library, Google AutoValue and Project Lombok:

• Generated the Builder pattern by default?
• Generated helper methods for, i.e., Optional and List?
• The number of lines of code to write?
• Required IDE's plugins?
• Are the objects immutable?

The three libraries are based on an annotation processor to generate/modify code for us:

• Immutable classes
• equals, hashCode and toString methods
• other utilities

NOTE: Immutables and AutoValue generate new classes with the processor, and Lombok modifies the bytecode of the original class.

💡 Overview

Immutables Java annotation processors to generate simple, safe, and consistent value objects. Do not repeat yourself, try Immutables, the most comprehensive tool in this field!

AutoValue provides an easier way to create immutable value classes, with a lot less code and less room for error, while not restricting your freedom to code almost any aspect of your class exactly the way you want it.

Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java.
Never write another getter or equals method again, with one annotation your class has a fully-featured builder, Automate your logging variables, and much more.

📇 The Model

We are going to create a class using the three libraries to be able to create an object representation with the following fields.

Optional<Integer> myOptional;
String myString;
List<String> myList;

🔩 Creating the model with AutoValue

package autovalue;

import com.google.auto.value.AutoValue;

import java.util.List;
import java.util.Optional;

@AutoValue
public abstract class MyModel {
    public abstract Optional<Integer> myOptional();

    public abstract String myString();

    public abstract List<String> myList();

    // Builder not generated by default
    // We have to write this boilerplate code
    @AutoValue.Builder
    public abstract static class Builder {
        public abstract Builder setMyOptional(Optional<Integer> myOptional);

        public abstract Builder setMyString(String myString);

        public abstract Builder setMyList(List<String> myList);

        public abstract MyModel build();
    }
}

• Generated the Builder pattern by default? 🔴
• Generated helper methods for, i.e., Optional and List? 🔴 Let's see in the next section
• The number of lines of code to write? 28 ✅
• It requires IDE plugin 🔴
• Are the objects immutable? 🔴 Let's see in the next section

🔩 Creating the model with Lombok

package lombok;

import java.util.List;
import java.util.Optional;

@Value
@Builder
public class MyModel {
    Optional<Integer> myOptional;

    String myString;

    List<String> myList;
}

• Generated the Builder pattern by default? 🔴
• Generated helper methods for, i.e., Optional and List? 🔴 Let's see in the next section
• The number of lines of code to write? 14 ✅
• It requires IDE plugins 🔴
• Are the objects immutable? 🔴 Let's see in the next section

🔩 Creating the model with Immutables

package immutables;

import org.immutables.value.Value;

import java.util.List;
import java.util.Optional;

@Value.Immutable
public interface MyModel {
    Optional<Integer> myOptional();

    String myString();

    List<String> myList();
}

• Generated the Builder pattern by default? ✅
• Generated helper methods for, i.e., Optional and List? ✅, Let's see in the next section
• The number of lines of code to write? 15 ✅
• It doesn't require IDE plugin ✅
• Are the objects immutable? ✅, Let's see in the next section

🌵Tests

Let's check some Pseudo-code:

We are going to create two identical lists with the same element inside:

list1=List.of("OneValue")
list2=List.of("OneValue")

We are going to create two identical value objects like this:

MyModel1: (
  myOptional=Optional.of(1)
  myString="Hello"
  myList=list1 // Using list 1
)

MyModel2: (
  myOptional=Optional.of(1)
  myString="Hello"
  myList=list2 // Using list 2
)

Even when using different references for the lists, the objects should be equal by value.

model1 == model2 // TRUE

After mutating one of the lists, the comparison of the objects should be the same

list1.add("AnotherValue")

model1 == model2 // TRUE

🍭 Testing AutoValue

@Test
void immutability() {
    // Create 2 lists containing the same element
    var myList1 = new ArrayList<String>();
    myList1.add("OneValue");
    var myList2 = List.of("OneValue");

    // Create model 1, assigning the list1
    var myModel1 = new AutoValue_MyModel.Builder()
            .setMyOptional(Optional.of(1)) // 😥 🔴 No helper for Optional
            .setMyString("Hello")
            .setMyList(myList1) // 😥 🔴 No helper for List
            .build();

    // Create model 2, assigning the list2
    var myModel2 = new AutoValue_MyModel.Builder() // 😥 🔴 No helper for copying
            .setMyOptional(Optional.of(1))
            .setMyString("Hello")
            .setMyList(myList2)
            .build();

    // Compare the 2 objects
    // Test passes since the fields contain the same values
    assertThat(myModel1).isEqualTo(myModel2);

    // Mutate the list used on Model 1
    myList1.add("AnotherValue");

    // Compare the 2 objects:
    // - PASSES objects are NOT equal for AutoValue 😮 🔴
    assertThat(myModel1).isNotEqualTo(myModel2);
}

🍭 Testing Lombok

@Test
void immutability() {
    // Create a mutable list with 1 element
    var myList1 = new ArrayList<String>();
    myList1.add("OneValue");
    var myList2 = List.of("OneValue");

    // Create model 1, assigning the list1
    var myModel1 = MyModel.builder()
            .myOptional(Optional.of(1)) // 😥 🔴 No helper for Optional
            .myString("Hello")
            .myList(myList1) // 😥 🔴 No helper for List
            .build();

    // Create model 2, assigning the list2
    var myModel2 = MyModel.builder() 😥 🔴 // No helper for copying
            .myOptional(Optional.of(1))
            .myString("Hello")
            .myList(myList2)
            .build();

    // Compare the 2 objects
    // Test passes since the fields contain the same values
    assertThat(myModel1).isEqualTo(myModel2);

    // Mutate the list used on Model 1
    myList1.add("AnotherValue");

    // Compare the 2 objects:
    // - PASSES objects are NOT equal for Lombok 😮 🔴
    assertThat(myModel1).isNotEqualTo(myModel2);
}

🍭 Testing Immutables

@Test
void immutability() {
   // Create a mutable list with 1 element
   var myList1 = new ArrayList<String>();
    myList1.add("OneValue");
    var myList2 = List.of("OneValue");

   // Create model 1, assigning the list1
   var myModel1 = ImmutableMyModel.builder()
           .myOptional(1) // 🎩 ✅ Helper for Optional
           .myString("Hello")
           .myList(myList1)
           .build();

   // Create model 2, assigning the list2
   var myModel2 = ImmutableMyModel.builder()
           .from(myModel1) // 🎩 ✅ Helper for copying
           .addMyList("OneValue") // 🎩 ✅ Helper for List
           .build();

   // Compare the 2 objects
   // Test passes since the fields contain the same values
   assertThat(myModel1).isEqualTo(myModel2);

   // Mutate the list used on Model 1
   myList1.add("AnotherValue");

   // Compare the 2 objects:
   // - Test PASSES objects ARE EQUAL for Immutables 🎩 ✅
   assertThat(myModel1).isEqualTo(myModel2);
}

📈 Results

	AutoValue	Lombok	Immutables
Line of Code to write/maintain	28	14	15
Builder (by default)	🔴	🔴	✅
Required IDE Plugin	✅	🔴	✅
Immutability	🔴	🔴	✅
Helper for Optional	🔴	🔴	✅
Helper for Collections	🔴	🔴	✅
Helper for Copying	🔴	🔴	✅

The code and the tests for the above examples are available on GitHub:

cchacin / immutables-autovalue-lombok

☕️ Immutables/AutoValue/Lombok 🔥 Which One?

☕️ Immutables/AutoValue/Lombok 🔥 Which One?

Blog post: https://dev.to/cchacin/immutables-autovalue-lombok-which-one-2j33

View on GitHub

🔆 Conclusions

• Even when the three libraries are doing a great job to avoid the boilerplate code, I personally use the Immutables library in most of the projects because of the safe defaults.

• To be fair, both Lombok and AutoValue can achieve also immutability but it requires paying more attention when creating the classes and that can cause problems.

• One main advantage of AutoValue is that it generates less code and that would be convenient if you are developing on/for Android.

• The configuration options for AutoValue and Lombok are pretty limited compared with Immutables but that topic was not covered in this article.

• Lombok requires a plugin if you want to be able to see all the modified/added methods to the bytecode.

Comments

[José Ramón (JR)]

You might want to check the vavr functional library. It has monads like Scala and it doesn't use annotations.

[Canem Inops]

Hey Carlos,

From the final table I feel that your method to compare these libraries were: get all features that I care in Immutables and compare with the others.
It is your space and you have the right, but I don't think that is fair to the readers.

I'm more familiar with Lombok and there are some goods parts that are absent here. For instance?

• If I don't want a builder? If my class has 3 attributes I don't really need a builder. How do I do that with the others? Will still be the same amount of boiler plate?

• About "helper for copying": an builder in Lombok creates a toBuilder method that allows you to make a builder with all values, change the ones you want and rebuild the object.

• Having an abstract class/interface defining your model, how these play together with jackson or hibernate where you have to annotate your class, how does it work?

• What about if my fields are made of mutable fields, will Immutable still be immutable by default?

I don't even know the answer for all these questions but I think a fairer comparison would try to go beyond the set of features that your favorite library offers.

[Carlos Chacin ☕👽]

Hi Canem,

Thank you for reading the post and adding your comments and feedback.

As mentioned in the post, this is a comparison of some of the three libraries' features, not an extensive review of every single feature.

In this article, we will compare some of the features of the Immutables.org library, Google AutoValue, and Project Lombok:

The particular set of evaluated features is based on the features that I consider essential for my use cases and are also defined at the beginning of the post.

Answering your question below:

If I don't want a builder? If my class has 3 attributes I don't really need a builder. How do I do that with the others? Will still be the same amount of boiler plate?

Immutables is even more flexible than Lombok in that case, allowing you to choose between a simple constructor with the parameters, but also a static factory method

• About "helper for copying": an builder in Lombok creates a toBuilder method that allows you to make a builder with all values, change the ones you want and rebuild the object.

Good catch, Even when I do not evaluate that in the comparison, I'll remove the java comment in the lombok example.

• Having an abstract class/interface defining your model, how these play together with jackson or hibernate where you have to annotate your class, how does it work?

For Hibernate/JPA, I do not use these libraries, IIRC the JPA standard requires JavaBeans mutable objects. But I do use them in particular for De/Serialization with Jackson, Jsonb, Gson, etc. and those play well with Interfaces and abstract classes.

• What about if my fields are made of mutable fields, will Immutable still be immutable by default?

Yes, and that is one of the critical aspects of the library, AutoValue and Lombok generate shallowly immutable classes.

There are a lot of additional features in the Immutables library that I consider useful. Lombok and AutoValue are not providing those, but I agree with the fact that it depends on the need and uses cases.
The three libraries work pretty well, and if you don't need any additional features from the immutables library, AutoValue and Lombok are also valid options.

[Carlos Chacin ☕👽]

I just checked the Lombok generated code and I cannot see the utility method for copying/cloning:

$ javap MyModel$MyModelBuilder

public class lombok2.MyModel$MyModelBuilder {
  lombok2.MyModel$MyModelBuilder();
  public lombok2.MyModel$MyModelBuilder myOptional(java.util.Optional<java.lang.Integer>);
  public lombok2.MyModel$MyModelBuilder myString(java.lang.String);
  public lombok2.MyModel$MyModelBuilder myList(java.util.List<java.lang.String>);
  public lombok2.MyModel build();
  public java.lang.String toString();
}

Can you point me to an example or documentation around that?

[Mikka]

Its some time now, but maybe it still helps. The copy-function of lombok is @With, which creates a copy with one property changed.

For your example it might be something like
myModel1.withMyString("other string")
which will create a copy of myModel1 with the changed myString value.

Thats what I also like about lombok, that you can use just the parts you need. Immutable is hard to use for legacy code, since you need to adapt all at once, while lombok leaves you with the chance to enhance classes with just the stuff you need. Copy a class? Add @With to it. Want a builder? Add @Builder to a class. Get rid of existing getters and setters? Just add @Getter and/or @Setter to it and delete whats already there.

[Mikka]

With lombok you could still generate code for JPA entities, since you can chose what you want to use, e.g. getters, setters, constructors, etc. Of cause there are pitfalls to watch out for, but it is usable, since it doesn't turn it immutable automatically.

[am312]

In Testing Immutables you're not comparing a mutated myList1 vs myList2 like you did in the previous tests.

[Carlos Chacin ☕👽]

Hi am312, good catch, that variable is not actually used in the Immutables example, I'll update the example to remove that. Thanks

[am312]

in order to do an apples-to-apples comparison, shouldn't you be using it? I guess you're trying to demonstrate if the libraries are doing a deep comparison of the collections' contained objects or just testing for ==.

[Ben Frey]

I'm curious why you expect two objects which contain different lists to be equal? That is certainly not intuitive. Does Immutables allow for configuring deep equals comparisons?

[Eric Ndouakulu Kiaku Mbuta]

Hey Carlos,

Why you don't test JAVA 14 record feature ?