Java: An Operational Semantics - Columbia University

Java: An Operational Semantics Gaurav S. Kc B. Eng. Project Department of Computing Semantics of Java -- why? Semantics: Assignment of meanings to programs Java: A simple, object-oriented, distributed, interpreted, robust, secure, architecture

neutral, portable, high-performance, multithreaded, and dynamic language. Why? contd. Better mental model of language Acceptance reliability expected behaviour Java : Security v.s. functionality

Widespread use Reasoning: towards a compromise Project Goals Semantics extension Better understanding of Java Research based -- no implementation

Break-down into parts Existing features: inheritance instance variables overloading and overriding Additions: access modifiers final, static, abstract constructors An example in the new syntax

abstract class Animal extends Object { int age; Animal() { super();} int getAge() {...} } public final class Dog extends Animal { final int legs = 4; final static boolean hasTail = yes; Dog() { this(Laika); } Dog(String s) { super(); } int getAge(String name) {} } Access Modifiers

Public Protected Private [default] No packages Semantics extension ...

Accessibility checks Final and Abstract modifier Classes sub-classing not permitted instantiating not permitted Fields Constant behaviour? Semantics extension ...

Well-formedness Constructor invocation Assignment Static modifier Fields that dont belong to objects Class and interface fields State extension: Class/interface entries

References Semantics extension ... Runtime checks Class or interface v.s. object Constructor A constructor is used in the creation of an object that is an instance of a class. It is the basis with which the run-time system allocates space from memory to objects during execution.

Instance fields & [inherited] instance fields OutOfMemory exception Static initialisation Syntax of a Constructor Explicit constructor invocation this(); same class

super(); parent class static initialisation Statements public class C extends B { int x = 5; public C (int n) { this(true); print(n);

} private C (boolean b) { super(); if (b) } } Constructor execution new C(true); [boolean] C(true), [] B(); x=5; if (b) , Other research work on Java

Within the Department of Computing: Exceptions [email protected] Concurrency [email protected] Binary Compatibility [email protected] In other research institutions: Generics [email protected] Security Issues

[email protected] Other research, contd. A comparison perhaps? Different aspects of Java Post-grad & post-doc work Conclusions Boring? Certainly not! Acquired skills Taste of pure research Lots of non-trivial work

State of the art technology Continued research in Java Semantics Improved know-how of the Java system Acknowledgements

Krysia Broda Sophia Drossopoulou Susan Eisenbach Tanya Valkevych