aalborg media lab 21-jun-15 software design lecture 1 “ introduction to java and oop”

Aalborg Media LabApr 18, 2023

Software Design

Lecture 1

“ Introduction to Java and OOP”


Lecture Overview

• Chapter 1.4 -1.6 of “Java Software Solutions”

• Slides and exercises can be found on: http://www.media.aau.dk/sd


Java Fundamentals

• Java is a object oriented language• Java is accompanied by the

“Java standard library ”• Java can be executed using the web• Is constantly under development

Chapter 1.4


A simple Java Application//**************************************************// Application printing a single line in console//**************************************************class HelloDan{ public static void main(String args[]) //entry point { System.out.println (“What’s the frequency Kenneth?”); }}


Java’s Structure

• Every Java application consists of class definitions• In the Java programming language:

– A program is made up of one or more classes

– A class contains one or more methods

– A method contains program statements

• A Java application always contains a method called main (entry point)


Using Objects

• The System.out object represents a destination to which we can send output

• In the HelloDan program, we invoked the println method of the System.out object:

System.out.println ("What’s the frequency Kenneth?");

object methodinformation provided to the method(parameters)


Using Comments

• Comments allow programmers to communicate their thoughts independent of the code

• Serves as documentation, VERY IMPORTANT !!

• Comments are “inline documentation”

// this is a single line comment

/* This is a block comment

*/


Identifiers and Reserved Words

• Language consists of identifiers– Words we make up

– Words another programmer did choose(for example when using the Java standard library)

– Reserved words

• Java is case sensitive– Class start with capital letter

– Methods start with small letter


Code Style

• Use descriptive names

• Make your code readable by using blank spaces and new lines(Listing 1.2 & 1.3)


About languages

• All programs must be translated to machine language in order to be executed and each type of CPU has its own specific binary machine language (01101…)

• There are four programming language levels:– machine language– assembly language– high-level language– fourth-generation language

Chapter 1.5


Compiler & Interpreters 1/2

• Compilers are small programs translating a language (source code) into another language (target language)

• Interpreters interweaves translation and execution(one line at a time)


Compiler


Java Using Compiler & Interpreter


Syntax & Semantic

• The syntax rules of a language define how we can put together symbols, reserved words, and identifiers to make a valid program

• The semantics of a program statement define what that statement means (its purpose or role in a program)

• A program that is syntactically correct is not necessarily logically (semantically) correct

• A program will always do what we tell it to do, not what we meant to tell it to do


Errors

• The compiler will find syntax errors and other basic problems (compile-time errors)

– If compile-time errors exist, an executable version of the program is not created

• A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)

• A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)


Environment

• JDK– compile and execute

• BlueJ (editor)– writing the code


Compiling and Execution

• The JDK and a simple Editor (Notepad) are enough for coding, compiling and execution


BlueJ Environment

• Java based development environment for Java

• BlueJhttp://www.bluej.org/download/download.html

http://www.bluej.org/download/download.html


Object-Oriented Programming

• Object is fundamental entity in Java

• Developing software by defining objects that interact with each other

• OOP is mapping real life situations into a program– Mapping objects and their behavior

Chapter 1.6


Problem Solving

• Life cycle of program development– Understand the problem– Design a solution– Considering alternatives / refining– Implementing the solution– Testing / fixing / refining the solution


Concepts/Terminology of OOP

• Object (real object of the problem domain)

• Attribute (characteristics of objects, state)

• Method (objects behavior)

• Class (objects are defined trough classes, concept)– Multiple object can be created from a class

• Encapsulation– Only object itself can change his state (manages itself)

• Inheritance– Reuse of class concepts for similar classes

• Polymorphism


Inheritance

Bank Account

Account

Charge Account

Savings Account

Checking Account

•One class can be used to derive another via inheritance•Classes can be organized into inheritance hierarchies


Exercises

• Use BlueJ for following exercises– JSS 1.1

– JSS 1.3

• Try out the Hello application (BlueJ demos)– Add method stop, printing “Bye, world”.

aalborg media lab 21-jun-15 software design lecture 1 “ introduction to java and oop”

Documents

aalborg media lab

java programming language

java fundamentals java

compiler slide

object oriented language

java standard library

oop slide

time slide