Object and reference immutability using java generics

A compiler-checked immutability guarantee provides useful documentation, facilitates reasoning, and enables optimizations. This paper presents Immutability Generic Java (IGJ), a novel language extension that expresses immutability without changing Java's syntax by building upon Java's generics and annotation mechanisms. In IGJ, each class has one additional type parameter that is Mutable, Immutable, or ReadOnly. IGJ guarantees both reference immutability (only mutable references can mutate an object) and object immutability (an immutable reference points to an immutable object). IGJ is the first proposal for enforcing object immutability within Java's syntax and type system, and its reference immutability is more expressive than previous work. IGJ also permits covariant changes of type parameters in a type-safe manner, e.g., a readonly list of integers is a subtype of a readonly list of numbers. IGJ extends Java's type system with a few simple rules. We formalize t...

• Type: Conference
• Year: 2007
• Where: SIGSOFT
• Authors: Yoav Zibin, Alex Potanin, Mahmood Ali, Shay Artzi, Adam Kiezun, Michael D. Ernst
• Keywords: Immutability Generic Java, Object Immutability, Reference Immutability, SIGSOFT 2007, Software Engineering