Object Oriented Programming

Autumn 2003

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Outline

Course organizationIntroductionJava overview

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Course goals

Software design vs hackingAbstractions vs language (syntax)Java used to illustrate conceptsNOT a course about JavaPrerequisites

knowledge of C, C++, or similarsome programming experience

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Staff

Lecturer: Timour Katchaounov(Timour.Katchaounov@it.uu.se)

Assistants (seminars, labs):Jesper Wilhelmsson(Jesper.Wilhelmsson@it.uu.se)

Ruslan Fomkin(Ruslan.Fomkin@it.uu.se)

E-mail subject: “OOP-HT03: xxx”

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Course resourcesAll course information (schedule, slides, etc.):http://www.csd.uu.se/datalogi/cmtrl/oop/ht03/

Course management system:Everyone should registerAccessible from university networkhttp://udblserv.it.uu.se:8080/oop_ht03

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Assignments

Voluntary Java assignmentAfter the lab assumed to ‘know’ Java

Pasture simulationFour assignments - 4 pointsExtra fifth assignment - 5 points

2 students per group

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LiteratureCourse:Barbara Liskov: Program Development in Java.

Java:Bruce Eckel: Thinking in Javawww.bruceeckel.comJava Language/API docs:

java.sun.comdeveloper.java.sun.comjava.sun.com/docs/books/tutorial

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Outline

Course organizationIntroductionJava overview

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Software design

Real systems are bigApache: ~50000 linesCommunicator 4: ~3 000 000 lines

Requires many people to cooperateHard to understand, develop, maintainNeed for methods to handle complexity

=> Decomposition and abstraction

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Decomposition

Decompose problems into sub-problemsSame level of detailIndependentCombined solve the original problem

Break up a system into modules

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Abstraction

Ignore details => focus on important propertiesSimplify the problemMany-to-one mappingExamples: sets, numbers, humansDesign:abstract -> decompose -> abstract -> …

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Abstraction methods

Abstraction by parameterizationignore identity, focus on common propertiesmodule reusability

Abstraction by specificationignore implementation, focus on functionModule independence

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Types of abstractions (1)

Procedural abstractionsabstract some operationIntroduce new operations

Data abstractionsSets of ‘similar’ objects and their operationsOperations are relatedIntroduce new data types

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Types of abstractions (2)

Iteration abstractionsIgnore item storage & retrieval details

Type hierarchiesGroup similar/related abstractionsAllow to ignore differencesSubtypes/supertypes

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Types of abstractions (3)Combined use of parameterization and specificationAbstraction is language independentAny programming language can be usedObject-oriented languages make things easierThe data abstraction is central for OO programming and design

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Outline

Course organizationIntroductionJava overview

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Java overview

Reference implementation by SUNPlatform independentCompiled into bytecode (kind of assembler)Programs run on a virtual machine JVMAutomatic memory management -garbage collection

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OO abstractions in JavaSpecification => interfaces, javadoc, assertionsParameterization => methods, classes

Data abstractions => classes & objectsProcedural abstractions => methodsIteration abstractions => loops (for, while, do), iteratorsType hierarchies => class inheritance

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Java programs

Consist of classes and/or an interfacesCollections of proceduresData abstractions

No global variables, no “free” functionsEach class in its own fileInterface and implementation in one file (no .h files)

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Classes

Consist of fields and methodspublic class Square extends Shape {

private float xCoordinate;…public void rotate(float degree) {…

}…}

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Java TypesClasses - system and user definedPrimitive types - system defined:

byte, short, int, long, (8,16,32,64 bit), boolean, char (16 bit), float, doublefor performanceCan be wrapped in classes

Arrays:Are objects<type>[] <name>;String names[];Can’t grow

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Objects and variablesData accessed through variablesContain objects (on heap) or values (on stack)Primitive and reference variablesObject creation - the new operatorEquality: ‘==‘ and ‘equals’Object identityMutability and sharingArray objects

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Class fieldsDescribe state of objects and classes<visibility> <type> <name> = <value>;public float xCoordinate = 74.3;Accessed through objectssomeObject.fieldNameStatic fileds - value shared by all class objectsstatic <visibility> <type> <name> = <value>;Accessed through class: someClass.fieldName

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Methods

Method declaration and creation<visibility> <return type> <name>(formal params)

{ body; }

Call semanticsexpr.someMethod(param1, …);

Class vs instance methodsConstructor methods

Initialize objectsUsed through new operator

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Packages

Group related classes and interfacesProvide for modularityClass/interface visibilityFully qualified names

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Known syntax

for, while, doswitchNo gotoNo pointers

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Java applications

Console applicationsGUI applicationsStandalone vs. applets

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Java applications:the main method

Entry point to run applicationsStatic public main(String[] args){…}One per class

testingalternative program versions

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Java applications:minimal Java programclass hello {

public static void main (String[] args) {

System.out.println(“Hello world!”);System.exit(0);

}}