Glacier helps keep your immutable data immutable.

What does Glacier do?

Glacier enforces transitive class immutability in Java.

• Transitive: if a class is immutable, then every field must be immutable. This means that all reachable state from an immutable object’s fields is immutable
• Class: the immutability of an object depends only on its class’s immutability declaration.
• Immutability: state in an object is not changable through any reference to the object.

Is Glacier ready to use?

Glacier works, but it has very limited knowledge of which JDK classes are immutable. You can help! Check out the source code, edit src/edu/cmu/cs/glacier/jdk.astub with annotations for the classes you care about, and submit a pull request.

How do I use Glacier?

A Glacier binary release is available!

1. Add the Glacier Maven repository to your list of repositories: http://www.cs.cmu.edu/~mcoblenz/maven2
2. Add a dependency on Glacier. The component is edu.cmu.cs.glacier:glacier:0.1.
3. Add the Glacier annotation processor to your build configuration (edu.cmu.cs.glacier.GlacierChecker).
4. Annotate your immutable classes with @Immutable. You will need to import edu.cmu.cs.glacier.qual.Immutable.
5. Build.

For example, here is a simple bogus class that you can use for testing. If everything is working, Glacier will report an error:

import edu.cmu.cs.glacier.qual.*;

@Immutable public class BogusImmutable {
    java.util.Date d;
}

Publications

Glacier has been shown to help users express and enforce immutability, preventing bugs. Please take a look at our paper:

Michael Coblenz, Whitney Nelson, Jonathan Aldrich, Brad Myers, and Joshua Sunshine. 2017. Glacier: transitive class immutability for Java. In Proceedings of the 39th International Conference on Software Engineering (ICSE ‘17), May 20 - 28, 2017, 496-506. ACM DL

Michael Coblenz, Joshua Sunshine, Jonathan Aldrich, Brad Myers, Sam Weber, Forrest Shull, “Exploring Language Support for Immutability” ICSE’2016: The 38th International Conference on Software Engineering, Austin, TX, May 14 - 22, 2016. pp. 736-747. ACM DL

Michael Coblenz, Joshua Sunshine, Brad Myers, Sam Weber, Forrest Shull, “Comparing Transitive to Non-Transitive Object Immutability”, The Sixth Workshop on Evaluation and Usability of Programming Languages and Tools (PLATEAU’2015), at SPLASH 2015, October 26, 2015, Pittsburgh, PA, pp. 47-48. ACM DL

If you want to replicate the study, you can use the same materials we did. You’ll need to install IntelliJ (we used IntelliJ IDEA Community 2016.2) and JDK 1.8 separately. Replication Package