Java Non-Null Types Language Extension

Extends the Java 1.4 frontend

Non-null types is a type-based approach to detect possible null pointer violations in code statically at compile time. Fähndrich and Leino showed how an object-oriented language such as Java or C# could be extended with non-null types. We have extended a Java compiler, in a modular way, to include non-null types. This is an example of how a large JastAdd project can be extended in an easy and declarative way. We have also implemented an inference algorithm to retrofit legacy code to include non-null types.

This project builds on the Java 1.4 Frontend. The front-end and the JastAdd system are bundled with the non-null source archives. The project uses Apache Ant as build system.

A draft presenting the implementation is available in:
Modular implementation of non-null types for Java, Torbjörn Ekman and Görel Hedin, Submitted for publication, Available in pdf

The work by Fähndrich and Leino is available in:
Declaring and Checking Non-Null Types in an Object-Oriented Language, Manuel Fähndrich and Rustan Leino, Proceedings of the 18th ACM Conference on Object-Oriented Programming Systems, Languages, and Applications, Anaheim, CA, October 2003, Available in pdf

Non-Null Types

• NonNullTypes-src.jar for downloading the example to your computer. Unjar the archive to extract the NonNullTypes and Java1.4Frontend folders. An included build file for Apache Ant is discussed below.
• JavaChecker.java is the main class that performs static semantic analysis for Java including non-null types.
• NonNull.ast extends the AST with new node types to represent non-null types and modifiers.
• NonNull.jrag extends the semantic analysis phase with non-null types. This is the main implementation with inline comments and is further discussed in the draft-paper above.
• tests There are a few test-cases in the tests folder. Each test is a single .java file with a matching .result file holding the expected output. RunTests.java collects and executes all test cases.
• build.xml: Ant build file to be used from a terminal window and from Eclipse. Makes use of tools and source files in the Java 1.4 Frontend component.
  • Use the targets build (default), test, and clean, when working from a terminal window. For example, type

    ant	generate all java files and compile them
    ant test	run all test cases
    ant clean	remove all generated files and all the class files for both generated and handwritten java files

  • Use the targets gen and cleanGen when working from eclipse (see Running JastAdd Under Eclipse):

    ant gen	generate all java files
    ant cleanGen	remove all generated files and their class files.