Java: An Operational Java: An Operational Semantics Semantics - - PowerPoint PPT Presentation

Java: An Operational Java: An Operational Semantics Semantics

Gaurav Gaurav S.

• S. Kc

Kc B.

• B. Eng
• Eng. Project

. Project Department of Computing Department of Computing

Semantics of Java Semantics of Java --

• - why?

why?

• Semantics:

Semantics:

– – Assignment of meanings to programs Assignment of meanings to programs

• Java:

Java:

– – A simple, object A simple, object-

• oriented, distributed,
• riented, distributed,

interpreted, interpreted, robust robust, , secure secure, architecture , architecture neutral, portable, high neutral, portable, high-

• performance,

performance, multithreaded, and dynamic language. multithreaded, and dynamic language.

Why? … contd. Why? … contd.

• Better “mental model” of language

Better “mental model” of language

• Acceptance

Acceptance

– – reliability reliability – – expected behaviour expected behaviour

• Java : Security v.s. functionality

Java : Security v.s. functionality

• Widespread use

Widespread use

• Reasoning: towards a compromise

Reasoning: towards a compromise

Project Goals Project Goals

• Semantics extension

Semantics extension

• Better understanding of Java

Better understanding of Java

• Research based

Research based --

• - no implementation

no implementation

Break Break-

• down into parts

down into parts

• Existing features:

Existing features:

– – inheritance inheritance – – instance variables instance variables – – overloading and overriding

• verloading and overriding
• Additions:

Additions:

– – access modifiers access modifiers – – final, static, abstract final, static, abstract – – constructors constructors

An example in the new syntax An example in the new syntax

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

Access Modifiers Access Modifiers

• Public

Public

• Protected

Protected

• Private

Private

• [default]

[default]

• No packages

No packages

• Accessibility checks

Accessibility checks

Semantics extension ...

Final and Abstract modifier Final and Abstract modifier

• Classes

Classes

– – sub sub-

• classing not permitted

classing not permitted – – instantiating not permitted instantiating not permitted

• Fields

Fields

– – Constant behaviour? Constant behaviour?

• Well

Well-

• formedness

formedness

• Constructor invocation

Constructor invocation

• Assignment

Assignment

Semantics extension ...

Static modifier Static modifier

• Fields that don’t belong to objects

Fields that don’t belong to objects

• Class and interface fields

Class and interface fields

• State extension:

State extension:

– – Class/interface entries Class/interface entries – – References References

• Runtime checks

Runtime checks

• Class or interface v.s. object

Class or interface v.s. object

Semantics extension ...

Constructor Constructor

A A constructor constructor is used in the creation of an is used in the creation of an

• bject that is an instance of a class.
• bject that is an instance of a class.

It is the basis with which the run It is the basis with which the run-

• time

time system allocates space from memory to system allocates space from memory to

• bjects during execution.
• bjects during execution.

Instance fields & [inherited] instance fields

Instance fields & [inherited] instance fields

OutOfMemory

OutOfMemory exception exception

Static initialisation

Static initialisation

Syntax of a Constructor Syntax of a Constructor

• Explicit constructor

Explicit constructor invocation invocation

– – this(); this();

same class

same class

– – super(); super();

parent class

parent class

static initialisation

static initialisation

• Statements

Statements

public class public class C C extends extends B { B { int int x = 5; x = 5; public public C ( C (int int n) { n) { this this( (true true); ); print(n); print(n); } } private private C ( C (boolean boolean b) { b) { super super(); (); if if (b) … (b) … } } } }

[boolean] C(true), σ [] B(); x=5; if (b) …, σ

Constructor Constructor execution execution

new C(true);

Other research work on Java Other research work on Java

• Within the Department of Computing:

Within the Department of Computing:

– – Exceptions Exceptions SLURP SLURP@ @DoC DoC – – Concurrency Concurrency SLURP SLURP@ @DoC DoC – – Binary Compatibility Binary Compatibility SLURP SLURP@ @DoC DoC

• In other research institutions:

In other research institutions:

– – Generics Generics PLT PLT@Rice @Rice – – Security Issues Security Issues SIP SIP@Princeton @Princeton

Other research, … Other research, … contd contd. .

• A comparison perhaps?

A comparison perhaps?

– – Different aspects of Java Different aspects of Java – – Post Post-

• grad & post

grad & post-

• doc work

doc work

Conclusions Conclusions

• Boring? Certainly not!

Boring? Certainly not!

• Acquired skills

Acquired skills

• Taste of pure research

Taste of pure research

• Lots of non

Lots of non-

• trivial work

trivial work

• State of the art technology

State of the art technology

• Continued research in Java Semantics

Continued research in Java Semantics

• Improved know

Improved know-

• how of the Java system

how of the Java system

Acknowledgements Acknowledgements

• Krysia Broda

Krysia Broda

• Sophia

Sophia Drossopoulou Drossopoulou

• Susan

Susan Eisenbach Eisenbach

• Tanya

Tanya Valkevych Valkevych